Existing Annotations Review

Core Functions

Mobile floral stimulus (florigen) that, at the shoot apical meristem, acts as a transcriptional co-regulator within the florigen activation complex (FT + FD-class bZIP factors + 14-3-3 proteins) to activate floral meristem identity genes and promote flowering. FT itself does not bind DNA but enables target-gene activation through its bZIP partners.

Molecular Function:

transcription coactivator activity

Directly Involved In:

positive regulation of flower development

Cellular Locations:

nucleus

Supporting Evidence:

file:ARATH/FT/FT-deep-research-falcon.md
FT is **not an enzyme** and does not catalyze a chemical reaction. Instead, it functions as a **mobile signaling protein/transcriptional co-regulator** that promotes flowering by forming protein complexes at the SAM with DNA-binding transcription factors.
file:ARATH/FT/FT-deep-research-falcon.md
Reviews emphasize that PEBP-family proteins such as FT do **not bind DNA directly**, but act through interaction with transcriptional regulators such as bZIP factors in the FD class.

Binds the FD/FDP bZIP DNA-binding transcription factors (and redundant partners such as AREB3) at the shoot apical meristem, recruiting them into the florigen activation complex that reprograms gene expression toward floral fate.

Molecular Function:

DNA-binding transcription factor binding

Directly Involved In:

meristem determinacy

Cellular Locations:

nucleus

Supporting Evidence:

file:ARATH/FT/FT-deep-research-falcon.md
At the **shoot apical meristem**, FT participates in complexes that reprogram gene expression toward floral fate, including activation of floral meristem identity programs.

Phosphatidylethanolamine-binding protein (PEBP) family member; the conserved PEBP/anion-binding fold is the biochemical/structural basis that distinguishes the FT activator from the antagonistic TFL1 repressor and underlies integration of photoperiodic flowering signals after synthesis in leaf phloem companion cells.

Molecular Function:

phosphatidylethanolamine binding

Directly Involved In:

photoperiodism, flowering

Cellular Locations:

cytoplasm

Supporting Evidence:

file:ARATH/FT/FT-deep-research-falcon.md
The antagonistic PEBP-family member **TFL1** is described as opposing FT function at shared FD-bound targets, effectively tuning floral induction by competition at the SAM.

References

GO_REF:0000043

Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping

Electronic GO annotation derived from mapping of UniProtKB/Swiss-Prot keywords (e.g. flowering-related keywords) to GO terms for FT; supports generic process-level annotations.

GO_REF:0000044

Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt.

Electronic GO annotation derived from UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping; FT is annotated to cytoplasm and nucleus consistent with a mobile florigen carrying both leaf-source cytoplasmic and SAM-nuclear pools.

PMID:10583960

A pair of related genes with antagonistic roles in mediating flowering signals.

FT promotes flowering and is positively regulated by CONSTANS (CO) in the long-day photoperiodic pathway; loss of FT delays flowering and overexpression causes precocious, CO/photoperiod-independent flowering.

"FT, together with LFY, promotes flowering and is positively regulated by CO. Loss of FT causes delay in flowering, whereas overexpression of FT results in precocious flowering independent of CO or photoperiod."
FT acts in part downstream of CO and mediates flowering signals antagonistically with its paralog TERMINAL FLOWER1 (TFL1), establishing the FT/TFL1 antagonism that tunes the floral transition.

"FT acts in part downstream of CO and mediates signals for flowering in an antagonistic manner with its homologous gene, TERMINAL FLOWER1 (TFL1)."

PMID:10583961

Activation tagging of the floral inducer FT.

FT was isolated by activation tagging as a floral inducer acting in parallel with the meristem-identity gene LEAFY (LFY), partially downstream of CONSTANS (CO).

"FLOWERING LOCUS T (FT), which acts in parallel with the meristem-identity gene LEAFY (LFY) to induce flowering of Arabidopsis, was isolated by activation tagging. Like LFY, FT acts partially downstream of CONSTANS (CO), which promotes flowering in response to long days."
The deduced FT protein sequence is similar to TERMINAL FLOWER1 (an inhibitor of flowering) and to membrane-associated mammalian PEBP-family proteins; FT does not directly control transcription or transcript processing, foreshadowing its role as a non-DNA-binding signaling protein.

"Unlike many other floral regulators, the deduced sequence of the FT protein does not suggest that it directly controls transcription or transcript processing. Instead, it is similar to the sequence of TERMINAL FLOWER 1 (TFL1), an inhibitor of flowering that also shares sequence similarity with membrane-associated mammalian proteins."

PMID:16099979

FD, a bZIP protein mediating signals from the floral pathway integrator FT at the shoot apex.

FT and the bZIP transcription factor FD are interdependent partners (via protein interaction) that act together at the shoot apex to promote floral transition, providing the molecular basis for FT's transcription-coactivator role.

"FD and FT are interdependent partners through protein interaction and act at the shoot apex to promote floral transition and to initiate floral development through transcriptional activation of a floral meristem identity gene, APETALA1 (AP1)."
The FT/FD complex transcriptionally activates APETALA1 (AP1), a floral meristem-identity gene, providing direct support for FT involvement in positive regulation of flower development.

"FD and FT are interdependent partners through protein interaction and act at the shoot apex to promote floral transition and to initiate floral development through transcriptional activation of a floral meristem identity gene, APETALA1 (AP1)."
FT mRNA is expressed in the vasculature of cotyledons and leaves, while FD is preferentially expressed in the shoot apex, consistent with FT being a leaf-derived long-distance signal that meets its bZIP partner at the apex.

"FLOWERING LOCUS T (FT) is a conserved promoter of flowering that acts downstream of various regulatory pathways, including one that mediates photoperiodic induction through CONSTANS (CO), and is expressed in the vasculature of cotyledons and leaves. A bZIP transcription factor, FD, preferentially expressed in the shoot apex is required for FT to promote flowering."

PMID:16099980

Integration of spatial and temporal information during floral induction in Arabidopsis.

A primary response to floral induction is activation of FT RNA expression in leaves; because flowers form at the distant shoot apex, FT (a small, possibly mobile protein) integrates temporal information for flowering.

"A primary response to floral induction is the activation of FT RNA expression in leaves. Because flowers form at a distant site, the shoot apex, these data suggest that FT primarily controls the timing of flowering."
A complex of FT and FD proteins activates floral identity genes such as APETALA1 (AP1), confirming the FT-FD activation module mediates floral meristem identity transcription.

"A complex of FT and FD proteins in turn can activate floral identity genes such as APETALA1 (AP1)."

PMID:17189287

Molecular basis of late-flowering phenotype caused by dominant epi-alleles of the FWA locus in Arabidopsis.

Ectopic FWA blocks the flowering pathway at or downstream of FT, with FWA binding to FT (yeast two-hybrid and pull-down) suggesting FWA delays flowering by interfering with FT/FD complex formation.

"The previous reports that fwa suppressed the precocious-flowering phenotype of plants overexpressing FLOWERING LOCUS T (FT) suggest that the flowering pathway(s) either at and/or downstream of FT is blocked by FWA."

PMID:17446353

FT protein movement contributes to long-distance signaling in floral induction of Arabidopsis.

FT mRNA is required only transiently in the leaf; FT fusion proteins expressed specifically in phloem cells move to the apex and across grafts, providing direct evidence that FT protein acts as a long-distance (florigenic) signal.

"We found that FT messenger RNA is required only transiently in the leaf. In addition, FT fusion proteins expressed specifically in phloem cells move to the apex and move long distances between grafted plants."
FT does not activate an intermediate messenger in leaves; therefore FT protein itself constitutes the long-distance signal that induces Arabidopsis flowering.

"we provide evidence that FT does not activate an intermediate messenger in leaves. We conclude that FT protein acts as a long-distance signal that induces Arabidopsis flowering."

PMID:19656342

Genetic and spatial interactions between FT, TSF and SVP during the early stages of floral induction in Arabidopsis.

FT and its paralog TSF redundantly mediate photoperiodic flowering; the ft tsf double mutant is photoperiod-insensitive and fully suppresses the early-flowering phenotype of CO overexpression.

"we show that FT and the closely related TSF are not essential for flowering, but that the double mutant is photoperiod-insensitive. Inactivation of both genes also fully suppresses the early-flowering phenotype caused by over-expression of constans (CO), a transcriptional regulator in the photoperiod pathway."
FT and TSF interact with the same bZIP transcription factors (FD/FDP-class) in yeast, demonstrating shared biochemical function as transcription-coactivator partners of bZIPs.

"we demonstrate that TSF and FT have similar biochemical functions by showing that they interact in yeast with the same bZIP transcription factors."
Phloem-companion-cell-specific FT or TSF expression rescues flowering in ft tsf double mutants, demonstrating that FT need not be expressed in the meristem and is loaded into the phloem from companion cells.

"Expression of FT or TSF from promoters specific for phloem companion cells drives early flowering of the double mutant, so no expression of either gene is required in the meristem."
FT and TSF are repressed by the MADS-box transcription factor SVP, integrating SVP repression into the FT/TSF photoperiodic flowering pathway.

"TSF, like FT, is repressed by SVP"

PMID:20626659

Arabidopsis BLADE-ON-PETIOLE1 and 2 promote floral meristem fate and determinacy in a previously undefined pathway targeting APETALA1 and AGAMOUS-LIKE24.

BOP1/2 promote floral meristem identity by upregulating APETALA1 via direct interactions with TGA bZIP transcription factors at the AP1 promoter, defining a parallel pathway to FT/FD that converges on AP1.

"BOP1/2 are recruited to the promoter of AP1 through direct interactions with TGA bZIP transcription factors"
BOP1/2, LFY and AP1 converge to down-regulate flowering-time regulators including AGAMOUS-LIKE24 in stage 2 floral meristems, providing context for how the FT/FD-AP1 pathway is fine-tuned by parallel inputs.

"all three activities converge to down-regulate flowering-time regulators including AGAMOUS-LIKE24 in stage 2 floral meristems"

PMID:21737277

FLOWERING LOCUS T regulates stomatal opening.

FT is expressed in guard cells and regulates stomatal opening downstream of phototropin (phot1/phot2) blue-light signaling, indicating an additional, non-floral role for FT in guard cells.

"FLOWERING LOCUS T (FT) is expressed in guard cells and regulates stomatal opening."
The scs1-1 (elf3 phot1 phot2) suppressor shows open stomata with high H+-ATPase activity, linking FT/ELF3 to guard-cell H+-ATPase activation; supports an annotation of FT to stomatal-opening regulation as a non-core/clock-output role.

"scs1-1 (elf3 phot1 phot2 triple mutant) had an open-stomata phenotype with high H(+)-ATPase activity"

PMID:22529749

FTIP1 is an essential regulator required for florigen transport.

FT-INTERACTING PROTEIN 1 (FTIP1), an ER membrane protein, is essential for FT protein transport to the shoot apex in Arabidopsis; loss of FTIP1 causes late flowering under long days partly via compromised FT movement, establishing that florigen transport is a regulated process.

"FT-INTERACTING PROTEIN 1 (FTIP1), is an essential regulator required for FT protein transport in Arabidopsis. Loss of function of FTIP1 exhibits late flowering under long days, which is partly due to the compromised FT movement to the shoot apex."
FTIP1 and FT share similar mRNA expression patterns and subcellular localization and interact directly, indicating an active loading/trafficking mechanism for FT in phloem companion cells.

"FTIP1 and FT share similar mRNA expression patterns and subcellular localization, and they interact"

PMID:29259105

Characterization of Multiple C2 Domain and Transmembrane Region Proteins in Arabidopsis.

Systematic characterization of the 16-member Arabidopsis MCTP family confirms that MCTP1 (FTIP1) C2 domains cooperate to regulate FTIP1's role in FT-dependent flowering-time control, supporting the regulated trafficking of FT.

"We further analyze in vivo effects of three C2 domains on the regulatory role of MCTP1 (FTIP1) in flowering time control in Arabidopsis, demonstrating that these C2 domains may be cooperative to mediate FTIP1 function during the floral transition."

PMID:30943325

Genetic interactions reveal the antagonistic roles of FT/TSF and TFL1 in the determination of inflorescence meristem identity in Arabidopsis.

FT/TSF and TFL1 act antagonistically in inflorescence meristem identity: ft tsf mutants generate a hyper-vegetative shoot (like TFL1 overexpression) while FT or TSF overexpression generates a terminal flower (like tfl1 mutants), placing FT in inflorescence-meristem identity control.

"The ft-10 tsf-1 mutants produced a compact inflorescence surrounded by serrated leaves (hyper-vegetative shoot) at the early bolting stage, as did plants overexpressing TFL1. Plants overexpressing FT or TSF (or both FT and TFL1) generated a terminal flower, as did tfl1-20 mutants."
Grafting demonstrates that long-distance FT signal from a 35S::FT rootstock restores normal inflorescence patterning to ft tsf scions, confirming FT functions as a mobile florigen in inflorescence meristem identity.

"Grafting ft-10 tsf-1 or ft-10 tsf-1 tfl1-20 mutant scions to 35S::FT rootstock plants produced a normal inflorescence and a terminal flower in the scion plants, respectively"

file:ARATH/FT/FT-deep-research-perplexity-lite.md

Deep research on FT function

Synthesis of the FT literature - FT is a leaf-produced mobile floral stimulus (florigen) that, after long-distance transport through the phloem, partners with FD-class bZIP transcription factors at the shoot apex to activate floral meristem-identity genes (AP1, SOC1, LFY).

file:ARATH/FT/FT-deep-research-falcon.md

Falcon (Edison Scientific) deep research on Arabidopsis FT (florigen) function, transport, and mode of action at the shoot apical meristem

"In *Arabidopsis*, **FT encodes a mobile protein signal** produced in leaves that is transported to the SAM, where it triggers the vegetative-to-reproductive phase transition."
"FT is **not an enzyme** and does not catalyze a chemical reaction. Instead, it functions as a **mobile signaling protein/transcriptional co-regulator** that promotes flowering by forming protein complexes at the SAM with DNA-binding transcription factors."
"Reviews emphasize that PEBP-family proteins such as FT do **not bind DNA directly**, but act through interaction with transcriptional regulators such as bZIP factors in the FD class."
"FT expression is activated in leaf **phloem companion cells (CCs)** under inductive conditions (notably long days), and the **FT protein is loaded into sieve elements (SEs)** for phloem transport."
"Once in the SEs, FT traffics through the **phloem stream** to the shoot. This movement is considered regulated, not a simple diffusion process."
"At the **shoot apical meristem**, FT participates in complexes that reprogram gene expression toward floral fate, including activation of floral meristem identity programs."
"The antagonistic PEBP-family member **TFL1** is described as opposing FT function at shared FD-bound targets, effectively tuning floral induction by competition at the SAM."
"CO directly activates **FT** transcription in leaves; FT is the key floral pathway integrator under long days"

Suggested Experiments

Experiment: In planta FT/FD/14-3-3 complex reconstitution and proximity-labeling (TurboID-FT or TurboID-FD) at the SAM in inductive long-day conditions, with parallel ChIP-seq for FT and FD at AP1/SOC1/LFY loci to map the in vivo florigen activation complex genome-wide.

Hypothesis: FT/FD/14-3-3 complexes assemble on a defined set of bZIP cis-elements at the SAM and are sufficient to convert vegetative shoot identity into floral meristem identity.

Type: Proximity labeling MS + ChIP-seq

Experiment: Domain-swap and structure-guided point mutagenesis in the FT anion-binding pocket (key residues including Tyr85, Gln140, the external loop) tested in 35S::FT lines for ability to promote vs delay flowering, paired with CRISPR-engineering of equivalent residues in TFL1.

Hypothesis: A small set of residues in the PEBP anion-binding pocket and external loop determines activator (FT) versus repressor (TFL1) activity at shared FD/bZIP targets, allowing reversible interconversion of florigen and antiflorigen identities.

Type: Site-directed mutagenesis with floral transition phenotyping

Experiment: Live cell imaging of fluorescently tagged FT and FTIP1/MCTP variants in companion-cell/sieve-element regions of the leaf phloem during the floral transition, combined with grafting experiments using rootstocks expressing pCC2::FT-GFP to quantify movement kinetics in different mutants.

Hypothesis: FTIP1 and additional MCTP-family proteins act sequentially to load FT into sieve elements; loss of specific MCTPs blocks loading without affecting general phloem transport.

Type: Live cell imaging with grafting

Deep Research

Falcon

(FT-deep-research-falcon.md)

this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 25 citations 2 artifacts 2026-06-01T05:43:28.087970

Edison artifact artifact-00 (text/markdown)

## Context ID: pqac-00000013 Figure 1 from the review illustrates the main genetic pathways controlling flowering time in *Arabidopsis thaliana*. It depicts sev (image/png)

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Research report: Functional annotation of FLOWERING LOCUS T (FT) in Arabidopsis thaliana (UniProt Q9SXZ2, locus At1g65480)

1) Verification of correct gene/protein identity (mandatory disambiguation)

The target protein is FLOWERING LOCUS T (FT) from Arabidopsis thaliana, consistently described in recent authoritative literature as the canonical florigen and a member of the phosphatidylethanolamine-binding protein (PEBP) family. FT is produced in leaf vasculature (phloem companion cells) and acts at the shoot apical meristem (SAM) to induce flowering, matching the UniProt entry Q9SXZ2 and the expected PEBP-family context. (takagi2023photoperiodicfloweringin pages 1-2, maple2024floweringtimefrom pages 2-4, colleoni2024floweringtimegenes pages 1-2)

2) Key concepts and current understanding (definitions, mechanism, localization)

2.1 Florigen and FT as a systemic flowering signal

“Florigen” is now operationally equated with FT-family proteins in many flowering plants. In Arabidopsis, FT encodes a mobile protein signal produced in leaves that is transported to the SAM, where it triggers the vegetative-to-reproductive phase transition. (tsuji2024thefunctionof pages 1-2, takagi2023photoperiodicfloweringin pages 1-2, maple2024floweringtimefrom pages 2-4)

2.2 Primary molecular function of FT (what the protein does)

FT is not an enzyme and does not catalyze a chemical reaction. Instead, it functions as a mobile signaling protein/transcriptional co-regulator that promotes flowering by forming protein complexes at the SAM with DNA-binding transcription factors. Reviews emphasize that PEBP-family proteins such as FT do not bind DNA directly, but act through interaction with transcriptional regulators such as bZIP factors in the FD class. (colleoni2024floweringtimegenes pages 1-2, maple2024floweringtimefrom pages 2-4)

2.3 Tissue, cellular, and subcellular route: where FT is made and where it acts

Source tissue (production): FT expression is activated in leaf phloem companion cells (CCs) under inductive conditions (notably long days), and the FT protein is loaded into sieve elements (SEs) for phloem transport. (takagi2023photoperiodicfloweringin pages 1-2, maple2024floweringtimefrom pages 2-4)

Long-distance transport route: Once in the SEs, FT traffics through the phloem stream to the shoot. This movement is considered regulated, not a simple diffusion process. (maple2024floweringtimefrom pages 2-4)

Site of action: At the shoot apical meristem, FT participates in complexes that reprogram gene expression toward floral fate, including activation of floral meristem identity programs. (martignago2023thebziptranscription pages 1-2, takagi2023photoperiodicfloweringin pages 1-2, maple2024floweringtimefrom pages 2-4)

A current synthesis of the pathway architecture (including FT as a convergent integrator and the leaf→SAM signaling concept) is visually summarized in Maple et al. 2024 (Fig. 1), which depicts converging pathways regulating FT and the downstream activation of floral identity genes at the SAM. (maple2024floweringtimefrom media c4f89fee)

2.4 Protein complexes and key interactors: how FT induces flowering at the SAM

A widely accepted current model is that FT induces flowering by forming a “florigen activation complex” that includes:
- FT (the mobile PEBP-family florigen),
- FD and FD-related bZIP transcription factors, and
- 14-3-3 proteins.
This complex promotes transcriptional changes leading to floral induction. (maple2024floweringtimefrom pages 2-4, tsuji2024thefunctionof pages 6-7)

The antagonistic PEBP-family member TFL1 is described as opposing FT function at shared FD-bound targets, effectively tuning floral induction by competition at the SAM. (maple2024floweringtimefrom pages 2-4)

3) Recent developments and latest research (prioritized 2023–2024)

Recent reviews emphasize that FT’s leaf-to-phloem export and long-distance movement are actively controlled by specific trafficking components, refining earlier “FT simply moves in phloem” models:
- FTIP1: an ER membrane protein implicated in CC→SE movement via a continuous ER network across plasmodesmata. (maple2024floweringtimefrom pages 2-4)
- QKY and SYP121: described as facilitating export via an MCTP–SNARE/endosomal trafficking route from CCs to SEs. (maple2024floweringtimefrom pages 2-4)
- NaKR1: a heavy metal–associated domain protein described as regulating long-distance FT trafficking in the phloem stream. (maple2024floweringtimefrom pages 2-4)

These elements are presented as key mechanistic refinements in 2024 syntheses of flowering-time mechanisms. (maple2024floweringtimefrom pages 2-4)

3.2 Quantitative transport timing and localization at the SAM

A 2024 review summarizes grafting/induction evidence indicating that leaf-produced FT can reach the SAM on the order of ~12 hours, supporting a rapid systemic signaling role. (tsuji2024thefunctionof pages 5-6)

3.3 Expansion of FT-responsive bZIP network at the SAM (primary research)

A 2023 primary study (PLOS Genetics) refines the classical “FT acts via FD” concept by showing that the bZIP transcription factor AREB3 is expressed at the SAM in a pattern overlapping FD and contributes redundantly to FT signaling. Genetic analyses indicate that multiple florigen-interacting bZIPs (including FD, AREB3, and additional bZIPs such as FDP) can act redundantly in the SAM, implying FT signaling is distributed across a small bZIP network rather than a single obligate partner. (martignago2023thebziptranscription pages 1-2)

3.4 Updated understanding of environmental integration upstream of FT

A 2023 dedicated review describes FT expression as having a distinct spatiotemporal pattern in long-day laboratory conditions: high expression in distal leaf phloem companion cells and a dusk peak under 16 h light/8 h dark long days. FT induction correlates with flowering when day length exceeds ~12 hours and is described as dosage-dependent. (takagi2023photoperiodicfloweringin pages 1-2)

A 2024 synthesis also highlights additional environmental integration routes such as elevated temperature signaling through PIF4/PIF5/PIF7, with an exemplar warm condition of 27 °C promoting induction of the upstream module that drives FT. (maple2024floweringtimefrom pages 2-4)

4) Current applications and real-world implementations (2023–2024)

4.1 Flowering-time and architecture engineering via FT/TFL1 editing (quantitative 2024 example)

A 2024 Plant Molecular Biology study demonstrates a practical breeding-oriented application: multiplex CRISPR/Cas9 editing of FT and TFL1 family paralogs in petunia to generate compact, early-flowering plants. Quantitative results reported include:
- Earlier flowering: edited PhTFL1 knockout lines flowered ~18.5 days earlier than wild type.
- Compactness: PhTFL1 knockout internodes ~8.5–8.9 cm vs wild type ~13.18–15.5 cm.
- Branching: PhTFL1 knockout ~11 branches, PhFT knockout ~13.5 branches, vs wild type ~5.5 branches.
These trait shifts align with commercial ornamental needs (compact growth, reduced reliance on growth regulators, faster flowering). (abdulla2024crisprcas9mediatedmutagenesisof pages 8-11)

While this is not Arabidopsis FT per se, it is a direct real-world implementation of the conserved FT/TFL1–PEBP module that was discovered and mechanistically dissected in Arabidopsis. (colleoni2024floweringtimegenes pages 1-2, abdulla2024crisprcas9mediatedmutagenesisof pages 8-11)

4.2 Broader flowering-time engineering strategies and expert synthesis (2023)

A 2023 review on CRISPR applications in flowering-time engineering compiles numerous published cases (across crops and ornamentals) targeting FT/FT-like genes and related regulators. It highlights the feasibility of both gene knockout and targeted sequence edits (including amino-acid swaps known to invert FT/TFL1-like behavior), and it emphasizes practical considerations such as pleiotropy and the value of cis-regulatory tuning rather than complete loss-of-function of central mobile signals. (hodaei2023unlockingnature’sclock pages 8-9, hodaei2023unlockingnature’sclock pages 4-6)

5) Expert opinions/analysis and open questions

Recent authoritative reviews converge on several expert-level interpretations:

FT is central but not acting alone: While FT is a pivotal “integrator” and systemic signal, multiple regulatory layers govern (i) its transcriptional induction in leaf phloem tissues and (ii) its transport competence. (takagi2023photoperiodicfloweringin pages 1-2, maple2024floweringtimefrom pages 2-4)
Trafficking is a key control point: Current models emphasize that CC→SE export and long-distance movement depend on specialized components (FTIP1, QKY, SYP121, NaKR1), suggesting FT signaling capacity can be tuned at the level of intracellular/vascular trafficking as well as transcription. (maple2024floweringtimefrom pages 2-4, colleoni2024floweringtimegenes pages 2-4)
Mechanism at the SAM is modular: The florigen activation complex concept (FT + FD-class bZIPs + 14-3-3) is an organizing principle, but experimental genetics in 2023 indicate redundancy among bZIP partners (e.g., AREB3), arguing for a more distributed decoding module at the apex. (martignago2023thebziptranscription pages 1-2, maple2024floweringtimefrom pages 2-4)
Unloading/post-phloem movement remains less resolved: A 2024 synthesis notes that, despite progress on CC→SE export and phloem trafficking, how FT is unloaded and moved after phloem delivery to the apex is still not fully understood. (maple2024floweringtimefrom pages 2-4)

Evidence-backed summary table

The following table provides a compact annotation-oriented view (process, mechanism, location, and 2023–2024 evidence).

Process/Function	Mechanism/Key partners	Subcellular/tissue location (production, transport route, site of action)	Key recent evidence (2023–2024) with paper, DOI/URL, and publication month/year	Notable quantitative data points
Target identity / core molecular role	Arabidopsis FT is the canonical florigen and a PEBP-family protein; it does not bind DNA directly but acts as a transcriptional co-regulator with FD-class bZIP factors (colleoni2024floweringtimegenes pages 1-2, takagi2023photoperiodicfloweringin pages 1-2, maple2024floweringtimefrom pages 2-4)	Produced in leaf vasculature, then acts at the shoot apical meristem (SAM) (takagi2023photoperiodicfloweringin pages 1-2, maple2024floweringtimefrom pages 2-4)	Maple et al. Plant Physiology (Feb 2024), DOI: 10.1093/plphys/kiae109, https://doi.org/10.1093/plphys/kiae109; Takagi et al. Plant Communications (May 2023), DOI: 10.1016/j.xplc.2023.100552, https://doi.org/10.1016/j.xplc.2023.100552; Colleoni et al. J Exp Bot (Mar 2024), DOI: 10.1093/jxb/erae112, https://doi.org/10.1093/jxb/erae112 (colleoni2024floweringtimegenes pages 1-2, takagi2023photoperiodicfloweringin pages 1-2, maple2024floweringtimefrom pages 2-4)	No catalytic activity reported; FT acts as a mobile signaling protein rather than an enzyme/transporter (colleoni2024floweringtimegenes pages 1-2, takagi2023photoperiodicfloweringin pages 1-2)
Photoperiodic flowering induction	CO directly activates FT transcription in leaves; FT is the key floral pathway integrator under long days (takagi2023photoperiodicfloweringin pages 1-2, maple2024floweringtimefrom pages 2-4)	Strong expression in phloem companion cells of distal leaves; signal ultimately reaches SAM (takagi2023photoperiodicfloweringin pages 1-2, maple2024floweringtimefrom pages 2-4)	Takagi et al. Plant Communications (May 2023), https://doi.org/10.1016/j.xplc.2023.100552; Maple et al. Plant Physiology (Feb 2024), https://doi.org/10.1093/plphys/kiae109; Maple Figure 1 schematic (takagi2023photoperiodicfloweringin pages 1-2, maple2024floweringtimefrom pages 2-4, maple2024floweringtimefrom media c4f89fee)	Typical lab LD = 16 h light / 8 h dark; FT induction correlates with flowering when day length exceeds ~12 h; CO mRNA peaks about 16 h after dawn in LDs (takagi2023photoperiodicfloweringin pages 1-2, maple2024floweringtimefrom pages 2-4)
Long-distance mobile florigen signal	FT protein is loaded into sieve elements and carried through the phloem to the SAM; movement is regulated, not passive diffusion (maple2024floweringtimefrom pages 2-4, tsuji2024thefunctionof pages 5-6)	Production: leaf companion cells; route: companion cell → sieve element → phloem stream → shoot apex; site of action: SAM (tsuji2024thefunctionof pages 5-6, maple2024floweringtimefrom pages 2-4)	Tsuji & Sato Plant and Cell Physiology (Jan 2024), DOI: 10.1093/pcp/pcae001, https://doi.org/10.1093/pcp/pcae001; Maple et al. Plant Physiology (Feb 2024), https://doi.org/10.1093/plphys/kiae109 (tsuji2024thefunctionof pages 5-6, maple2024floweringtimefrom pages 2-4)	Grafting/induction experiments indicate leaf-produced FT can reach the SAM in about 12 h (tsuji2024thefunctionof pages 5-6)
Controlled export and trafficking	Export from companion cells requires FTIP1; QKY and SYP121 facilitate export via an MCTP-SNARE/endosomal trafficking route; long-distance trafficking is regulated by NaKR1 (maple2024floweringtimefrom pages 2-4, colleoni2024floweringtimegenes pages 2-4)	Companion cell ER/plasmodesmata interface, then sieve elements/phloem stream toward the apex (maple2024floweringtimefrom pages 2-4)	Maple et al. Plant Physiology (Feb 2024), https://doi.org/10.1093/plphys/kiae109; Colleoni et al. J Exp Bot (Mar 2024), https://doi.org/10.1093/jxb/erae112 (maple2024floweringtimefrom pages 2-4, colleoni2024floweringtimegenes pages 2-4)	Late flowering in ftip1/qky/mctp6 loss-of-function backgrounds is consistent with impaired FT transport, though no single numeric effect size is given in the excerpts (colleoni2024floweringtimegenes pages 2-4)
Site and mode of action at the SAM	FT forms a floral activation complex with FD/FD-related bZIPs and 14-3-3 proteins, promoting floral target genes such as AP1 and LFY; TFL1 antagonizes FT by competing for FD-associated function (takagi2023photoperiodicfloweringin pages 1-2, tsuji2024thefunctionof pages 6-7, maple2024floweringtimefrom pages 2-4)	FT accumulates in the shoot apex; activity is centered in/around the SAM and floral anlagen rather than peripheral leaf tissues (tsuji2024thefunctionof pages 5-6, maple2024floweringtimefrom pages 2-4)	Takagi et al. Plant Communications (May 2023), https://doi.org/10.1016/j.xplc.2023.100552; Tsuji & Sato Plant Cell Physiology (Jan 2024), https://doi.org/10.1093/pcp/pcae001; Maple et al. Plant Physiology (Feb 2024), https://doi.org/10.1093/plphys/kiae109 (tsuji2024thefunctionof pages 5-6, takagi2023photoperiodicfloweringin pages 1-2, tsuji2024thefunctionof pages 6-7, maple2024floweringtimefrom pages 2-4)	Imaging with SUC2::FT-GFP showed central accumulation at the apex; quantitative value not given in excerpt, but SAM localization is emphasized experimentally (tsuji2024thefunctionof pages 5-6)
Expanded FT-signaling transcription factor network	In addition to FD, AREB3 redundantly mediates FT signaling at the SAM; multiple florigen-interacting bZIPs contribute, refining the classic FT–FD-only model (martignago2023thebziptranscription pages 1-2, martignago2023thebziptranscription pages 20-21)	AREB3 expression overlaps FD in the SAM, where FT-dependent transcriptional reprogramming occurs (martignago2023thebziptranscription pages 1-2)	Martignago et al. PLOS Genetics (May 2023), DOI: 10.1371/journal.pgen.1010766, https://doi.org/10.1371/journal.pgen.1010766 (martignago2023thebziptranscription pages 1-2, martignago2023thebziptranscription pages 20-21)	Redundant genetic effects reported qualitatively: fd areb3 and higher-order bZIP mutant combinations flower later than single mutants; no exact flowering-day values in excerpt (martignago2023thebziptranscription pages 1-2)
Environmental modulation beyond photoperiod	FT expression is also promoted by PIF4/PIF5/PIF7 under warm conditions; thermosensory phyB-state changes can increase FT induction (maple2024floweringtimefrom pages 2-4)	Leaf tissues where FT is transcriptionally induced before systemic transport (maple2024floweringtimefrom pages 2-4)	Maple et al. Plant Physiology (Feb 2024), https://doi.org/10.1093/plphys/kiae109 (maple2024floweringtimefrom pages 2-4)	Elevated temperature example in review: 27 °C promotes PIF/CO-mediated FT induction relative to optimal ambient conditions (maple2024floweringtimefrom pages 2-4)
Transport/localization model support from recent schematic synthesis	Recent synthesis places FT at the center of converging flowering pathways and explicitly depicts transport from leaf to SAM, where floral identity genes are activated (maple2024floweringtimefrom media c4f89fee)	Leaf source tissue → mobile signal → green schematic SAM with floral integrators/identity genes (maple2024floweringtimefrom media c4f89fee)	Maple et al. Figure 1, Plant Physiology (Feb 2024), https://doi.org/10.1093/plphys/kiae109 (maple2024floweringtimefrom media c4f89fee)	Figure summarizes pathway convergence rather than providing new numeric measurements; useful as a current consensus model (maple2024floweringtimefrom media c4f89fee)

Table: This table summarizes the functional annotation of Arabidopsis thaliana FT (UniProt Q9SXZ2), focusing on molecular role, transport, site of action, partners, and recent 2023–2024 evidence. It is useful as a compact evidence-backed reference for FT biology and annotation.

Key sources (with URLs and publication dates)

Maple R. et al. Flowering time: From physiology, through genetics to mechanism. Plant Physiology. Feb 2024. https://doi.org/10.1093/plphys/kiae109 (maple2024floweringtimefrom pages 2-4)
Tsuji H., Sato M. The Function of Florigen in the Vegetative-to-Reproductive Phase Transition in and around the Shoot Apical Meristem. Plant and Cell Physiology. Jan 2024. https://doi.org/10.1093/pcp/pcae001 (tsuji2024thefunctionof pages 1-2)
Colleoni P.E. et al. Flowering time genes branching out. Journal of Experimental Botany. Advance Access 12 Mar 2024. https://doi.org/10.1093/jxb/erae112 (colleoni2024floweringtimegenes pages 1-2)
Takagi H. et al. Photoperiodic flowering in Arabidopsis: Multilayered regulatory mechanisms of CONSTANS and the florigen FLOWERING LOCUS T. Plant Communications. May 2023. https://doi.org/10.1016/j.xplc.2023.100552 (takagi2023photoperiodicfloweringin pages 1-2)
Martignago D. et al. AREB3 mediates FT signalling and floral transition at the Arabidopsis shoot apical meristem. PLOS Genetics. May 2023. https://doi.org/10.1371/journal.pgen.1010766 (martignago2023thebziptranscription pages 1-2)
Abdulla M.F. et al. CRISPR/Cas9-mediated mutagenesis of FT/TFL1 in petunia improves plant architecture and early flowering. Plant Molecular Biology. Jun 2024. https://doi.org/10.1007/s11103-024-01454-9 (abdulla2024crisprcas9mediatedmutagenesisof pages 8-11)

Notes on limitations of this report

This report focuses on experimentally supported functions and recent synthesis. Within the retrieved 2023–2024 sources, quantitative molecular biophysics (e.g., binding constants, FT protein concentrations in phloem) were not available in the extracted text, so quantitative reporting is primarily at the level of photoperiod/temperature regimes, timing of systemic movement, and applied phenotypic outcomes from gene-editing implementations. (tsuji2024thefunctionof pages 5-6, takagi2023photoperiodicfloweringin pages 1-2, maple2024floweringtimefrom pages 2-4, abdulla2024crisprcas9mediatedmutagenesisof pages 8-11)

References

(takagi2023photoperiodicfloweringin pages 1-2): Hiroshi Takagi, Andrew K. Hempton, and Takato Imaizumi. Photoperiodic flowering in arabidopsis: multilayered regulatory mechanisms of constans and the florigen flowering locus t. May 2023. URL: https://doi.org/10.1016/j.xplc.2023.100552, doi:10.1016/j.xplc.2023.100552. This article has 167 citations and is from a peer-reviewed journal.
(maple2024floweringtimefrom pages 2-4): Robert Maple, Pan Zhu, Jo Hepworth, Jia-Wei Wang, and Caroline Dean. Flowering time: from physiology, through genetics to mechanism. Plant Physiology, 195:190-212, Feb 2024. URL: https://doi.org/10.1093/plphys/kiae109, doi:10.1093/plphys/kiae109. This article has 119 citations and is from a highest quality peer-reviewed journal.
(colleoni2024floweringtimegenes pages 1-2): Pierangela E Colleoni, Sam W van Es, Ton Winkelmolen, Richard G H Immink, and G Wilma van Esse. Flowering time genes branching out. Journal of Experimental Botany, 75:4195-4209, Mar 2024. URL: https://doi.org/10.1093/jxb/erae112, doi:10.1093/jxb/erae112. This article has 30 citations and is from a domain leading peer-reviewed journal.
(tsuji2024thefunctionof pages 1-2): Hiroyuki Tsuji and Moeko Sato. The function of florigen in the vegetative-to-reproductive phase transition in and around the shoot apical meristem. Plant and Cell Physiology, 65:322-337, Jan 2024. URL: https://doi.org/10.1093/pcp/pcae001, doi:10.1093/pcp/pcae001. This article has 27 citations and is from a domain leading peer-reviewed journal.
(martignago2023thebziptranscription pages 1-2): Damiano Martignago, Vítor da Silveira Falavigna, Alessandra Lombardi, He Gao, Paolo Korwin Kurkowski, Massimo Galbiati, Chiara Tonelli, George Coupland, and Lucio Conti. The bzip transcription factor areb3 mediates ft signalling and floral transition at the arabidopsis shoot apical meristem. PLOS Genetics, 19:e1010766, May 2023. URL: https://doi.org/10.1371/journal.pgen.1010766, doi:10.1371/journal.pgen.1010766. This article has 33 citations and is from a domain leading peer-reviewed journal.
(maple2024floweringtimefrom media c4f89fee): Robert Maple, Pan Zhu, Jo Hepworth, Jia-Wei Wang, and Caroline Dean. Flowering time: from physiology, through genetics to mechanism. Plant Physiology, 195:190-212, Feb 2024. URL: https://doi.org/10.1093/plphys/kiae109, doi:10.1093/plphys/kiae109. This article has 119 citations and is from a highest quality peer-reviewed journal.
(tsuji2024thefunctionof pages 6-7): Hiroyuki Tsuji and Moeko Sato. The function of florigen in the vegetative-to-reproductive phase transition in and around the shoot apical meristem. Plant and Cell Physiology, 65:322-337, Jan 2024. URL: https://doi.org/10.1093/pcp/pcae001, doi:10.1093/pcp/pcae001. This article has 27 citations and is from a domain leading peer-reviewed journal.
(tsuji2024thefunctionof pages 5-6): Hiroyuki Tsuji and Moeko Sato. The function of florigen in the vegetative-to-reproductive phase transition in and around the shoot apical meristem. Plant and Cell Physiology, 65:322-337, Jan 2024. URL: https://doi.org/10.1093/pcp/pcae001, doi:10.1093/pcp/pcae001. This article has 27 citations and is from a domain leading peer-reviewed journal.
(abdulla2024crisprcas9mediatedmutagenesisof pages 8-11): Mohamed Farah Abdulla, Karam Mostafa, and Musa Kavas. Crispr/cas9-mediated mutagenesis of ft/tfl1 in petunia improves plant architecture and early flowering. Plant Molecular Biology, Jun 2024. URL: https://doi.org/10.1007/s11103-024-01454-9, doi:10.1007/s11103-024-01454-9. This article has 20 citations and is from a peer-reviewed journal.
(hodaei2023unlockingnature’sclock pages 8-9): Ashkan Hodaei and Stefaan P. O. Werbrouck. Unlocking nature’s clock: crispr technology in flowering time engineering. Plants, 12:4020, Nov 2023. URL: https://doi.org/10.3390/plants12234020, doi:10.3390/plants12234020. This article has 11 citations.
(hodaei2023unlockingnature’sclock pages 4-6): Ashkan Hodaei and Stefaan P. O. Werbrouck. Unlocking nature’s clock: crispr technology in flowering time engineering. Plants, 12:4020, Nov 2023. URL: https://doi.org/10.3390/plants12234020, doi:10.3390/plants12234020. This article has 11 citations.
(colleoni2024floweringtimegenes pages 2-4): Pierangela E Colleoni, Sam W van Es, Ton Winkelmolen, Richard G H Immink, and G Wilma van Esse. Flowering time genes branching out. Journal of Experimental Botany, 75:4195-4209, Mar 2024. URL: https://doi.org/10.1093/jxb/erae112, doi:10.1093/jxb/erae112. This article has 30 citations and is from a domain leading peer-reviewed journal.
(martignago2023thebziptranscription pages 20-21): Damiano Martignago, Vítor da Silveira Falavigna, Alessandra Lombardi, He Gao, Paolo Korwin Kurkowski, Massimo Galbiati, Chiara Tonelli, George Coupland, and Lucio Conti. The bzip transcription factor areb3 mediates ft signalling and floral transition at the arabidopsis shoot apical meristem. PLOS Genetics, 19:e1010766, May 2023. URL: https://doi.org/10.1371/journal.pgen.1010766, doi:10.1371/journal.pgen.1010766. This article has 33 citations and is from a domain leading peer-reviewed journal.

Artifacts

Edison artifact artifact-00

Citations

maple2024floweringtimefrom pages 2-4
tsuji2024thefunctionof pages 5-6
martignago2023thebziptranscription pages 1-2
takagi2023photoperiodicfloweringin pages 1-2
colleoni2024floweringtimegenes pages 2-4
tsuji2024thefunctionof pages 1-2
colleoni2024floweringtimegenes pages 1-2
tsuji2024thefunctionof pages 6-7
martignago2023thebziptranscription pages 20-21
https://doi.org/10.1093/plphys/kiae109;
https://doi.org/10.1016/j.xplc.2023.100552;
https://doi.org/10.1093/jxb/erae112
https://doi.org/10.1093/pcp/pcae001;
https://doi.org/10.1093/plphys/kiae109
https://doi.org/10.1371/journal.pgen.1010766
https://doi.org/10.1093/pcp/pcae001
https://doi.org/10.1016/j.xplc.2023.100552
https://doi.org/10.1007/s11103-024-01454-9
https://doi.org/10.1016/j.xplc.2023.100552,
https://doi.org/10.1093/plphys/kiae109,
https://doi.org/10.1093/jxb/erae112,
https://doi.org/10.1093/pcp/pcae001,
https://doi.org/10.1371/journal.pgen.1010766,
https://doi.org/10.1007/s11103-024-01454-9,
https://doi.org/10.3390/plants12234020,

Perplexity

(FT-deep-research-perplexity-lite.md)

**Key Concepts and Definitions** Perplexity sonar-pro 7 citations 2025-10-19T15:09:22.587543

The FT gene (FLOWERING LOCUS T, AT1G65480) in Arabidopsis thaliana encodes a small, highly conserved protein that acts as a central regulator of flowering time, functioning as the mobile florigenic signal that promotes the transition from vegetative growth to flowering in response to photoperiod cues[1][3][5][8].

Key Concepts and Definitions

Molecular Function:
FT encodes a phosphatidylethanolamine-binding protein (PEBP) family member[1][5]. Its primary molecular function is as a component of the mobile floral stimulus ("florigen"), which is synthesized in the phloem companion cells of leaves and transported to the shoot apical meristem[1][3][5][8]. There, FT interacts with transcription factors to activate floral meristem identity genes.
Biological Processes:
FT is a master regulator of the photoperiodic flowering pathway. It integrates environmental signals (mainly day length) and triggers the transition from vegetative to reproductive development[1][3][5][8]. FT is induced by long days and acts downstream of the CONSTANS (CO) gene, which is regulated by the circadian clock and light[1][3][7]. The FT-FD complex at the shoot apex activates MADS-box genes such as SOC1, FUL, AP1, and LFY, which are essential for floral induction[1].
Cellular Localization:
FT mRNA is expressed specifically in the companion cells of the phloem[1][3].
FT protein is a mobile signal: it moves through the phloem sieve elements to the shoot apical meristem, where it exerts its function[1][3][5][8].
At the shoot apex, FT is unloaded from the phloem and acts in the surrounding meristematic tissue[1][3].

Protein Domains

FT contains a PEBP domain, characteristic of the phosphatidylethanolamine-binding protein family[1][5]. This domain is responsible for its structural stability and interaction with partner proteins.

Known Interactions

FD and FDP:
FT physically interacts with the bZIP transcription factors FD and FD PARALOG (FDP) at the shoot apex to form a transcriptional activation complex[1][6][8]. This complex directly binds to promoters of floral meristem identity genes.
14-3-3 Proteins:
In some species (e.g., rice), the FT-FD interaction is mediated by 14-3-3 proteins, though in Arabidopsis, direct interaction is predominant[1].
Upstream Regulators:
FT expression is regulated by CONSTANS (CO) and GIGANTEA (GI), which integrate photoperiod and circadian signals[1][3][7].

Disease Associations

There are no known disease associations for FT in Arabidopsis or other plants, as it is not a disease gene but a developmental regulator. In animals, PEBP family proteins have been implicated in disease, but this is not the case for FT in plants[1][5].

Recent Developments and Applications (2023–2024)

Recent reviews and expression studies confirm the conserved role of FT orthologs in flowering regulation across plant species, with ongoing research into its expression dynamics and potential for crop improvement[9].
Manipulation of FT expression is a major strategy in agricultural biotechnology to control flowering time and improve yield in various crops[9].

Relevant Statistics and Data

FT is highly conserved among angiosperms, with orthologs present in most flowering plants[9].
Its expression is tightly regulated by photoperiod, with peak expression at dusk under long-day conditions, acting as a booster for flowering[7].

Expert Opinions and Analysis

FT is considered the long-sought florigen, a mobile signal that coordinates environmental sensing in leaves with developmental changes at the shoot apex[1][3][8].
The FT-FD complex is a paradigm for mobile protein signaling in plants, and its study has broad implications for understanding plant development and adaptation[1][3][8][9].

Citations (with URLs and Dates):

[1] Plant Physiology, "Floral Induction in Arabidopsis by FLOWERING LOCUS T Requires...", https://academic.oup.com/plphys/article/169/3/2187/6114284, 2015.
[3] PMC, "Photoperiodic Regulation of Florigen Function in Arabidopsis thaliana", https://pmc.ncbi.nlm.nih.gov/articles/PMC4489636/, 2015.
[5] UniProt, "FT - Protein FLOWERING LOCUS T", https://www.uniprot.org/uniprotkb/Q9SXZ2/entry, accessed 2024.
[6] CORE, "FT Protein Acts as a Long-Range Signal in Arabidopsis", https://core.ac.uk/outputs/81197980/, 2012.
[7] New Phytologist, "The FLOWERING LOCUS T gene expression is controlled by high...", https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.18932, 2023.
[8] Bohrium, "FT Protein Acts as a Long-Range Signal in Arabidopsis", https://www.bohrium.com/paper-details/ft-protein-acts-as-a-long-range-signal-in-arabidopsis/811990471252377602-4933, 2012.
[9] Frontiers in Plant Science, "Insight from expression profiles of FT orthologs in plants", https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2024.1397714/full, 2024.

Citations

https://academic.oup.com/plphys/article/169/3/2187/6114284,
https://pmc.ncbi.nlm.nih.gov/articles/PMC4489636/,
https://www.uniprot.org/uniprotkb/Q9SXZ2/entry,
https://core.ac.uk/outputs/81197980/,
https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.18932,
https://www.bohrium.com/paper-details/ft-protein-acts-as-a-long-range-signal-in-arabidopsis/811990471252377602-4933,
https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2024.1397714/full,

📚 Additional Documentation

Falcon Research

(FT-falcon-research.md)

Falcon Research Report: FT (ARATH)

Generated using FutureHouse Falcon API

Question: You are a molecular biologist and gene annotation expert conducting comprehensive research to support GO annotation curation.

Provide detailed, well-cited information focusing on:
1. Gene function and molecular mechanisms
2. Cellular localization and subcellular components
3. Biological processes involvement
4. Disease associations and phenotypes
5. Protein domains and structural features
6. Expression patterns and regulation
7. Evolutionary conservation
8. Key experimental evidence and literature

Format as a comprehensive research report with citations suitable for Gene Ontology annotation curation.

Research the Arabidopsis thaliana gene FT.

=== UNIPROT METADATA ===
UniProt ID: Q9SXZ2
Entry Name: FT_ARATH
Gene Name: FT
Locus Tag: At1g65480 {ECO:0000312|Araport:AT1G65480}
Protein Name: Protein FLOWERING LOCUS T
Organism: Arabidopsis thaliana (Mouse-ear cress)
NCBI Taxonomy ID: 3702
Function: Component of the mobile flower-promoting signal (floral stimulus or florigen). Promotes the transition from vegetative growth to flowering. Required for 'SEPALLATA3' (SEP3) and 'FRUITFULL' (FUL) accumulation in mature rosette leaves. Seems to acts in parallel with 'LEAFY' to induce flowering by regulating 'APETALA1'. Translated in leaves and then transported to the shoot apical meristem where it activates the transcription of several floral meristem identity genes. May play a role in both the autonomous and the long-day flowering pathways.
Subcellular Location: Cytoplasm
Subunit: Interacts with FD/BZIP14 and FDP/BZIP27 (PubMed:16099979, PubMed:16099980). Interacts with FTIP1/MCTP1 in phloem companion cells (PubMed:22529749, PubMed:29259105). Interacts with NAKR1 (PubMed:27255839).
======================

Provide a comprehensive report covering function, localization, processes, domains, disease associations, expression, conservation, and relevant GO terms.

IMPORTANT: Focus specifically on the gene identified by the metadata above, particularly the UniProt ID, locus tag, and protein description if provided.

Sometimes different genes in the same organism have the same name. In this case, the gene being reviewed is the one identified by the metadata above.

Below is the comprehensive research report on the Arabidopsis thaliana FT gene (UniProt Q9SXZ2, At1g65480), formatted in a style appropriate for Gene Ontology annotation curation. All statements are supported by literature from the provided context.

────────────────────────────────────────────────────────────────────────────
I. Abstract
The FLOWERING LOCUS T (FT) gene encodes a 20‐kDa protein belonging to the phosphatidylethanolamine‐binding protein (PEBP) family and functions as the mobile floral stimulus (florigen) in Arabidopsis thaliana. FT integrates environmental cues—most notably long-day photoperiods and temperature signals—with endogenous timing mechanisms to orchestrate the transition from vegetative to reproductive growth. Synthesized in the leaf cytoplasm, particularly in phloem companion cells, the FT protein is trafficked via the vascular system to the shoot apical meristem (SAM), where it interacts with bZIP transcription factors (FD, FDP) and other regulatory proteins (e.g., FTIP1, NAKR1) to initiate floral meristem identity gene expression. Its activity is tightly regulated at multiple levels including transcriptional activation by CONSTANS, chromatin remodeling, protein stability, and protein–protein interactions. Moreover, FT is evolutionarily conserved across angiosperms, underscoring its fundamental role in reproductive development. This report details FT’s gene function, localization, involvement in biological processes, phenotypic consequences of altered activity, its protein structural features, expression regulation, and the extensive experimental evidence underlying these findings (narayan2019analysisofthe pages 11-15, pin2012themultifacetedroles pages 2-3).

────────────────────────────────────────────────────────────────────────────
II. Introduction
Flowering is a decisive developmental event in the life cycle of plants and is tightly regulated by both external environmental cues and internal genetic programs. Arabidopsis thaliana has served as a model organism to dissect the molecular underpinnings of this transition, and at the centre of this regulatory network lies the FT gene. FT encodes a protein that serves as a mobile signal, or florigen, that is produced in the leaves and transported to the SAM—a process that ensures the synchrony of environmental response with developmental decision‐making (narayan2019analysisofthe pages 11-15, pin2012themultifacetedroles pages 2-3). The gene’s expression is modulated by the CONSTANS (CO) protein, which, under long-day conditions, induces FT transcription in a circadian‐regulated fashion. This temporal regulation is critical as it ensures that FT expression is coupled with the ideal light period for flowering induction (komeda2004geneticregulationof pages 6-8, turck2008regulationandidentity pages 6-8).

Over the past two decades, multiple studies have illuminated the network of genes and proteins that interact with FT, revealing its pivotal role not only in floral induction but also in coordinating other developmental processes such as shoot architecture and even certain aspects of stomatal regulation. The multifaceted roles of FT and its mode of action—as a protein that is synthesized in one tissue and acts in another—present a paradigm for non–cell‐autonomous signaling in plants. Such insights bear significant implications on how flowering time is controlled and have driven efforts toward detailed Gene Ontology (GO) annotations to capture these complexities (golembeski2015photoperiodicregulationof pages 10-11, lebedeva2020theevolutionaryaspects pages 1-2).

Because flowering time has a direct impact on seed production and crop yield, clarifying FT’s underlying molecular mechanisms promises to inform both basic developmental biology and applied agricultural practices. This report integrates evidence relating to FT’s gene function, cellular localization, involvement in core biological processes, structural features, expression patterns, evolutionary conservation, and key experiments validating its role, thereby providing a resource for refining GO annotation for FT in Arabidopsis thaliana (narayan2019analysisofthe pages 11-15, pin2012themultifacetedroles pages 2-3).

────────────────────────────────────────────────────────────────────────────
III. Gene Function and Molecular Mechanisms
FT functions as a master regulator of the flowering transition by transducing signals that arise from both the light environment and the plant’s internal clock. Under long-day conditions, the accumulation of CO in the leaf leads to the transcriptional activation of FT. Once the FT transcript is produced, the protein is synthesized in the cytoplasm of the phloem companion cells (narayan2019analysisofthe pages 11-15, pin2012themultifacetedroles pages 2-3). The integration of photoperiodic signals into FT expression is crucial; CO’s regulation by light and circadian rhythms ensures that FT is produced only when day-length conditions are optimal for flowering. As such, FT serves as the key output of the photoperiod pathway and links external light conditions to the developmental switch from vegetative to reproductive growth (komeda2004geneticregulationof pages 6-8, pin2012themultifacetedroles pages 2-3).

After synthesis, FT is exported from leaf cells via the phloem, and experimental grafting studies have demonstrated that its movement—not that of the mRNA—is required for flowering induction. This observation underscores the non–cell–autonomous nature of FT action. In the SAM, FT interacts with the bZIP transcription factor FD (and its homolog FDP) to form a complex known as the florigen activation complex (FAC). The FAC then binds to the promoters of floral meristem identity genes such as APETALA1 (AP1), FRUITFULL (FUL), and SEPALLATA3 (SEP3), ultimately committing the meristem to flower formation (golembeski2015photoperiodicregulationof pages 10-11, wigge2011ftamobile pages 2-3).

Regulatory feedback loops further refine FT activity. For instance, FT’s interaction with 14-3-3 adaptor proteins facilitates its nuclear import in conjunction with FD (narayan2019analysisofthe pages 15-19). Additionally, negative regulators such as TERMINAL FLOWER 1 (TFL1) compete with FT for FD binding, thereby delaying flowering when conditions are not ideal (golembeski2015photoperiodicregulationof pages 11-12, wickland2015thefloweringlocus pages 1-6). Post-translational control mechanisms play a role as well—FT protein stability is modulated by proteasome–dependent degradation, particularly through signals embedded in its C-terminal region, ensuring that its levels remain tightly correlated with updated environmental inputs (takagi2023photoperiodicfloweringin pages 13-14, narayan2019analysisofthe pages 15-19).

Chromatin-level regulation also factors into FT’s molecular control. Histone modifications, such as H3K27 trimethylation and H3K4 demethylation, are essential for maintaining the appropriate chromatin state of the FT locus, thus balancing activation and repression in response to developmental cues and environmental changes (pin2012themultifacetedroles pages 2-3, wigge2011ftamobile pages 2-3). In summary, FT operates as a molecular integrator, converting light signals via CO activation, ensuring proper spatial-temporal protein transport, and engaging in a network of protein–protein interactions to trigger the expression of floral identity genes—a process that is indispensable for the floral transition (narayan2019analysisofthe pages 11-15, golembeski2015photoperiodicregulationof pages 10-11, komeda2004geneticregulationof pages 6-8).

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IV. Cellular Localization and Subcellular Components
The spatial distribution of FT is critical for its function as a mobile flowering signal. FT mRNA is predominantly transcribed in the leaves, specifically in specialized phloem companion cells where it is targeted for translation (narayan2019analysisofthe pages 11-15, pin2012themultifacetedroles pages 2-3). Immunolocalization studies and cell fractionation experiments have confirmed that FT is localized in the cytoplasm within these cells, consistent with its initial synthesis in a non-nuclear compartment (takagi2023photoperiodicfloweringin pages 13-14).

Following synthesis, the mature FT protein is actively loaded into the sieve tube elements of the phloem. This loading process is mediated by interacting proteins such as FTIP1, which are essential for the translocation of FT through the vascular system (turck2008regulationandidentity pages 11-12, narayan2019analysisofthe pages 15-19). Once within the phloem, FT is capable of moving long distances by traveling via the plasmodesmata, thus ensuring that the signal reaches distal tissues like the shoot apical meristem (mathieu2007exportofft pages 1-2, matsoukas2015florigensandantiflorigens pages 3-5). At the SAM, the protein is imported into the nucleus where it interacts with FD; the nuclear localization of FD, a transcription factor, underscores the significance of FT’s regulated movement (turck2008regulationandidentity pages 11-12, wigge2011ftamobile pages 2-3).

The efficiency of FT transport may also be influenced by membrane-associated factors. For example, the interaction with FTIP1 suggests that FT may transiently associate with endomembrane systems, which could facilitate its movement from the phloem companion cells into the sieve elements (turck2008regulationandidentity pages 1-2, xu2012recentadvancesof pages 3-5). Additionally, evidence indicates that FT can interact with other proteins, such as NAKR1, which may modulate its subcellular trafficking and help direct the protein to its target site in the SAM (turck2008regulationandidentity pages 1-2, narayan2019analysisofthe pages 15-19).

Overall, FT’s subcellular distribution—from initial cytoplasmic synthesis in leaf cells, through its phloem-based transport, to its nuclear function in the SAM—illustrates how precise localization underpins its role as a systemic signal that coordinates developmental transitions in response to environmental inputs (turck2008regulationandidentity pages 11-12, mathieu2007exportofft pages 1-2).

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V. Biological Processes Involvement
FT is a central component in the regulation of flowering time—a process that is vital to plant reproductive success. It is at the core of the photoperiod pathway, where it integrates circadian clock signals with external light cues to promote the floral transition. Under long-day conditions, FT expression is induced following the accumulation of CONSTANS, and its subsequent translation and movement to the SAM ensure that floral meristem identity genes are activated precisely when environmental conditions are favorable (narayan2019analysisofthe pages 11-15, komeda2004geneticregulationof pages 6-8).

In the shoot apical meristem, the formation of a complex between FT and FD initiates a cascade of gene expression changes, including the upregulation of APETALA1 (AP1), FRUITFULL (FUL), and SEPALLATA3 (SEP3). These genes are responsible for determining floral organ identity, meaning that FT is indirectly responsible for defining the structure and function of the flower (wigge2011ftamobile pages 2-3, turck2008regulationandidentity pages 11-12). In this way, FT functions as a switch that reprograms the growth of the meristem from producing leaf primordia to generating floral buds (komeda2004geneticregulationof pages 6-8, golembeski2015photoperiodicregulationof pages 10-11).

Beyond its canonical role in flowering, FT also influences other aspects of plant development. It has been implicated in the regulation of shoot architecture, including lateral bud growth and branching, thereby contributing to overall plant morphology. For instance, FT-mediated suppression of axillary bud outgrowth ensures that resources are devoted to the production of a cohesive inflorescence rather than dispersing into the formation of additional vegetative structures (pin2012themultifacetedroles pages 3-7, pin2012themultifacetedroles pages 14-14). Moreover, emerging evidence suggests that FT may be involved in light-induced stomatal opening, linking photosynthetic efficiency and water regulation with developmental timing (pin2012themultifacetedroles pages 2-3, wigge2011ftamobile pages 1-2).

From an ecological and evolutionary perspective, the tight coordination between FT-regulated flowering and environmental cues such as daylength and temperature is essential for reproductive fitness. Flowering at the optimal time ensures efficient pollination and seed set, which are key for propagation in variable climates (lebedeva2020theevolutionaryaspects pages 1-2, putterill2016ftandflorigen pages 4-5). Thus, FT is not only a mediator of developmental timing but is also at the heart of how plants adapt to and exploit their environments for reproductive success (turck2008regulationandidentity pages 1-2, golembeski2015photoperiodicregulationof pages 10-11).

Collectively, the biological processes governed by FT encompass a spectrum of developmental events—from the transition to flowering to modulation of shoot architecture and stress responses—all of which are finely tuned to environmental signals. This functional versatility highlights the importance of FT as a central node in the plant’s developmental network (narayan2019analysisofthe pages 11-15, komeda2004geneticregulationof pages 6-8).

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VI. Disease Associations and Phenotypes
Although the term “disease” is not traditionally applied to plant developmental mutants, disruptions in FT function produce distinct phenotypes that can be considered deleterious, particularly in agricultural contexts. In Arabidopsis thaliana, loss-of-function mutants in FT display pronounced delays in flowering under inductive long-day conditions. Such delays can lead to extended vegetative growth periods, ultimately impacting reproductive success and yield. Conversely, constitutive or ectopic expression of FT results in precocious flowering and can lead to abnormal floral morphology, as well as alterations in overall shoot architecture (komeda2004geneticregulationof pages 6-8, wigge2011ftamobile pages 2-3).

These phenotypes underscore the importance of balanced FT expression. In controlled experiments, ft mutants have consistently exhibited a late flowering phenotype compared to wild-type plants, demonstrating the gene’s pivotal role in promoting the transition to flowering (komeda2004geneticregulationof pages 6-8, pin2012themultifacetedroles pages 2-3). In experimental contexts, precise manipulation of FT levels has been shown to either delay or accelerate flowering, a feature that has practical implications for crop breeding. Alterations in flowering time affect not only the developmental stage of the plant but may also influence fruit set and seed production—a relationship that can have broad economic impacts in agricultural systems (putterill2016ftandflorigen pages 1-2, mathieu2007exportofft pages 1-2).

Furthermore, the antagonistic dynamics between FT and TFL1 are critical for maintaining the balance between vegetative and reproductive growth. Because TFL1 functions as a repressor of flowering by competing with FT for binding partners, disruptions in their relative levels can result in profound morphological defects. Such imbalances could be harnessed to improve crop productivity; however, inadvertent perturbations may lead to developmental defects resembling “disease‐like” syndromes in plants (golembeski2015photoperiodicregulationof pages 11-12, wickland2015thefloweringlocus pages 1-6).

In summary, while FT is not associated with human disease in the strict sense, its misregulation in plants results in abnormal growth and developmental timing that can be detrimental to plant fitness and yield, mirroring the impact of disease phenotypes in other biological systems (komeda2004geneticregulationof pages 6-8, pin2012themultifacetedroles pages 2-3).

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VII. Protein Domains and Structural Features
FT is a member of the PEBP family, and its structural features reflect its function as a critical signaling molecule. Crystallographic and sequence analyses have revealed that FT possesses a highly conserved globular structure composed of a central β-sheet flanked by α-helices (turck2008regulationandidentity pages 6-8, turck2008regulationandidentity pages 11-12). This structural motif is essential not only for maintaining the integrity of the protein but also for mediating its interactions with other key regulatory partners such as FD and 14-3-3 proteins (narayan2019analysisofthe pages 15-19, wigge2011ftamobile pages 2-3).

Critical studies have identified specific amino acid residues within FT that are necessary for its activity as an inducer of flowering. For example, a tyrosine residue at position 134 and a tryptophan at position 138 have been shown to distinguish functional inducer FTs from repressor homologs, suggesting that these residues form part of an anion-binding pocket essential for FT’s biological activity (wickland2015thefloweringlocus pages 15-16, wickland2015thefloweringlocus pages 6-9). These conserved residues are maintained across FT homologs in diverse plant species, highlighting the evolutionary constraints imposed on the FT protein structure for its role in floral induction.

Further structural insights have come from studies examining the interactions between FT and its partners. The binding interface formed between FT and FD is critical for the assembly of the florigen activation complex, and surface features of FT—such as charge distribution and loop flexibility—are thought to facilitate this protein–protein interaction (narayan2019analysisofthe pages 15-19, turck2008regulationandidentity pages 8-9). Additionally, FT has been suggested to interact with lipid molecules; its phosphatidylethanolamine-binding capacity may influence its association with membrane compartments during transport (golembeski2015photoperiodicregulationof pages 11-12, wigge2011ftamobile pages 1-2).

The conservation of the PEBP fold in FT not only reinforces its functional role in flowering regulation but also provides a structural framework that can guide mutational analyses. By altering key residues or loops, researchers have been able to dissect the functional domains necessary for FT’s interaction with FD and other components, thereby further refining the models of FT function (wickland2015thefloweringlocus pages 15-16, wickland2015thefloweringlocus pages 6-9). This level of structural detail is indispensable for Gene Ontology annotations that seek to capture both the molecular function and the interaction capacity of FT in the context of non–cell–autonomous signaling (narayan2019analysisofthe pages 15-19, turck2008regulationandidentity pages 6-8).

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VIII. Expression Patterns and Regulation
FT expression is subject to a complex regulatory network that integrates temporal, spatial, and environmental cues. In Arabidopsis thaliana, FT is predominantly expressed in the leaves—especially within the phloem companion cells—under long-day photoperiodic conditions (narayan2019analysisofthe pages 11-15, komeda2004geneticregulationof pages 6-8). The transcription factor CONSTANS (CO) plays an indispensable role in this regulation: CO accumulates in the late afternoon when light conditions are favorable, binding to the FT promoter and activating transcription (pin2012themultifacetedroles pages 2-3, turck2008regulationandidentity pages 6-8). This finely tuned regulation underpins the entrainment of the circadian clock with flowering time, ensuring that FT expression peaks at the appropriate time of day.

The photoperiodic regulation of FT is further modulated by chromatin remodeling and epigenetic marks. Histone modifications such as acetylation and methylation influence the accessibility of the FT promoter, thereby amplifying or attenuating the transcriptional response to CO and other activators (pin2012themultifacetedroles pages 2-3, wigge2011ftamobile pages 2-3). These epigenetic mechanisms enable rapid adjustments in FT expression in response to shifts in environmental conditions, such as temperature fluctuations or changes in light quality (lebedeva2020theevolutionaryaspects pages 1-2, turck2008regulationandidentity pages 1-2).

Post-transcriptional regulation also plays a role; for instance, microRNAs and RNA-binding proteins have been implicated in the fine-tuning of FT mRNA stability, ensuring that only appropriate levels of the transcript are available for translation (narayan2019analysisofthe pages 15-19, wickland2015thefloweringlocus pages 9-12). In this context, although FT mRNA is confined to the tissue of synthesis, its protein product becomes the far–ranging signal that ultimately triggers flowering (mathieu2007exportofft pages 1-2, matsoukas2015florigensandantiflorigens pages 3-5).

Spatial regulation is critical as well. Although FT transcription is robust in the leaves, its function is exerted at the SAM, and experiments have shown that the transcript itself is not mobile; instead, the mobile FT protein, generated in leaves, is responsible for delivering the flowering signal (mathieu2007exportofft pages 1-2, matsoukas2015florigensandantiflorigens pages 3-5). This delineation between the site of mRNA production and the site of protein function is central to the non–cell–autonomous mechanism of FT action.

Additionally, light receptors such as phytochromes and cryptochromes have been found to influence FT expression indirectly through interactions with CO and other components of the light signaling network, thereby integrating external photic cues into the transcriptional regulation of FT (turck2008regulationandidentity pages 1-2, komeda2004geneticregulationof pages 6-8).

In summary, FT expression is orchestrated by a multilayered network comprising transcriptional activators, chromatin remodelers, post-transcriptional regulators, and light-sensing receptors. This coordinated regulation ensures that FT is expressed at the right time, in the right cells, and in the appropriate amounts to effectively initiate flowering (narayan2019analysisofthe pages 11-15, pin2012themultifacetedroles pages 2-3).

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IX. Evolutionary Conservation
The FT gene is one of the most highly conserved regulators of flowering in the plant kingdom. Homologs of FT have been identified in a wide range of angiosperms, from herbaceous dicots to major cereal crops, highlighting its primordial role in floral induction (lebedeva2020theevolutionaryaspects pages 1-2, putterill2016ftandflorigen pages 4-5). Cross-species functional studies have shown that FT-like proteins can substitute for Arabidopsis FT in mutant backgrounds, thereby restoring normal flowering time—even when derived from evolutionarily distant species (matsoukas2015florigensandantiflorigens pages 3-5, prewitt2021interspeciesfunctionalcompatibility pages 1-2).

In phylogenetic analyses, FT is grouped with other members of the PEBP family, such as TWIN SISTER OF FT (TSF) and TERMINAL FLOWER 1 (TFL1). Although TFL1 functions antagonistically by repressing flowering, the high sequence conservation among these family members underscores the evolutionary constraints on these proteins. Notably, specific residues critical for FT’s activity, such as those delineated in mutational studies (e.g., tyrosine 134 and tryptophan 138), are maintained across species, suggesting that the mechanism of flowering induction via FT is fundamentally conserved (wickland2015thefloweringlocus pages 15-16, wickland2015thefloweringlocus pages 6-9).

Additionally, the regulatory elements within the FT promoter that respond to photoperiod and environmental signals exhibit conservation across plant species, further reinforcing the notion that the underlying genetic circuitry for flowering is ancient and evolutionarily stable (golembeski2015photoperiodicregulationof pages 10-11, komeda2004geneticregulationof pages 6-8). The conservation of these cis-regulatory elements ensures that FT homologs retain a similar responsiveness to environmental conditions, thereby conferring adaptive advantages across diverse ecological niches.

The evolutionary conservation of FT extends beyond its sequence and regulatory elements to include its cellular behavior. The mechanism whereby FT is synthesized in leaves and transported to the SAM is a conserved trait among angiosperms, indicating that the non–cell–autonomous function of FT as a mobile signal is a deeply embedded evolutionary innovation (mathieu2007exportofft pages 1-2, matsoukas2015florigensandantiflorigens pages 3-5). This level of functional conservation not only validates FT’s role in flowering but also underscores its potential as an evolutionary benchmark for developing GO annotations in plant biology (putterill2016ftandflorigen pages 4-5, wickland2015thefloweringlocus pages 6-9).

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X. Key Experimental Evidence and Literature
Our current understanding of FT is built on a robust foundation of experimental evidence from diverse approaches. Seminal grafting experiments have unequivocally demonstrated that the FT protein, rather than its mRNA, is the transmissible signal required to induce flowering in recipient plants. In these experiments, the transfer of FT from donor to scion was sufficient to trigger floral development, providing strong evidence for its role as a mobile signal (mathieu2007exportofft pages 1-2, matsoukas2015florigensandantiflorigens pages 3-5).

Molecular interaction studies have been equally informative. Techniques such as yeast two-hybrid screening, co-immunoprecipitation, and Förster resonance energy transfer–fluorescence lifetime imaging microscopy (FRET-FLIM) have confirmed direct physical interactions between FT and key transcription factors like FD and FDP. These interactions are essential for the formation of the florigen activation complex that mediates the transcriptional activation of downstream floral meristem identity genes (narayan2019analysisofthe pages 15-19, turck2008regulationandidentity pages 11-12). Furthermore, mutant analyses provide compelling functional evidence: Arabidopsis ft mutants robustly display delayed flowering, while constitutive overexpression leads to precocious flowering—outcomes that unequivocally place FT at the heart of flowering regulation (komeda2004geneticregulationof pages 6-8, pin2012themultifacetedroles pages 2-3).

Structural studies have also advanced our understanding of FT. High-resolution X-ray crystallography has revealed that FT adopts a conserved PEBP fold; this conserved structure is critical for its interaction with both small ligands and protein partners. Mutagenesis studies focused on conserved residues have underscored the functional importance of the FT structure in mediating its signal transduction role (wickland2015thefloweringlocus pages 15-16, turck2008regulationandidentity pages 6-8).

Gene expression analyses, employing RNA sequencing and in situ hybridization, have established that FT is expressed predominantly in the phloem companion cells under long-day conditions. These spatial and temporal expression patterns have been further corroborated by promoter–GUS fusions and quantitative RT-PCR assays, which together provide a detailed picture of FT’s regulation in vivo (narayan2019analysisofthe pages 11-15, komeda2004geneticregulationof pages 6-8). Chromatin immunoprecipitation (ChIP) assays have also provided data on the epigenetic modifications at the FT locus, demonstrating that histone marks correlate with its activation status and linking environmental signals to chromatin state modulation (pin2012themultifacetedroles pages 2-3, wigge2011ftamobile pages 2-3).

Collectively, these diverse experimental approaches—from grafting and genetic mutant analysis to molecular interaction assays and structural biology—form a comprehensive body of evidence supporting the role of FT as a central regulator of flowering in Arabidopsis thaliana. This experimental foundation is critical for the accurate assignment of Gene Ontology terms to FT, ensuring that its annotated functions capture the complexity and integration of environmental and developmental signals (golembeski2015photoperiodicregulationof pages 10-11, mathieu2007exportofft pages 1-2, matsoukas2015florigensandantiflorigens pages 3-5).

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XI. Concluding Remarks
In summary, the FT gene (UniProt Q9SXZ2, At1g65480) in Arabidopsis thaliana is a linchpin of flowering regulation. Acting as the mobile florigen, FT is synthesized in the leaves and is translocated through the phloem to the shoot apical meristem, where it exerts its regulatory functions by interacting with transcription factors like FD. This interaction culminates in the activation of floral meristem identity genes and thus directly promotes the transition from vegetative to reproductive growth (narayan2019analysisofthe pages 11-15, wigge2011ftamobile pages 2-3).

FT’s function is governed by a multi-tiered regulatory network. At the transcriptional level, its expression is driven by the photoperiodic regulator CO, while chromatin modifications and post-transcriptional events further refine its transcriptional output. The post-translational fate of FT, including its stability and subcellular trafficking, ensures that its activity is both timely and spatially precise. Moreover, the dynamic balance between FT and antagonistic regulators such as TFL1 reinforces the need for tight control over the flowering process (komeda2004geneticregulationof pages 6-8, pin2012themultifacetedroles pages 2-3).

Protein structural studies have revealed that FT’s conserved PEBP fold and key amino acid residues are indispensable for its role as a mobile signal; these features underlie its capacity to interact with both partner proteins and, potentially, lipid molecules that may assist in its transport. The evolutionary conservation of FT, evident from its homologues in species ranging from cereals to woody perennials, further highlights its central role in orchestrating flowering across angiosperms (wickland2015thefloweringlocus pages 15-16, wickland2015thefloweringlocus pages 6-9).

The extensive experimental evidence—from grafting studies to molecular interaction assays and structural analyses—not only validates FT’s role but also provides a rich set of data for its GO annotation. Accurately capturing FT’s diverse functions, complex regulatory mechanisms, and non–cell–autonomous behavior in GO terms is crucial for advancing our overall understanding of plant developmental biology and for the practical manipulation of flowering times in crop improvement strategies (mathieu2007exportofft pages 1-2, matsoukas2015florigensandantiflorigens pages 3-5, turck2008regulationandidentity pages 1-2).

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XII. Future Outlook and Implications for Gene Ontology Annotation
Research on FT continues to yield novel insights into integrated signaling networks that determine flowering time. Future studies are poised to further elucidate the subtleties of FT transport mechanisms—possibly involving additional regulatory proteins, differential splicing variants, or interactions with cellular lipids—and to explore the interplay between FT-mediated signaling and other growth-regulatory pathways. This forthcoming research promises to refine existing models and thereby enhance the resolution of GO annotations for FT and other florigenic components (narayan2019analysisofthe pages 81-85, wickland2015thefloweringlocus pages 6-9).

The continued acclimatization of plants to changing environmental conditions through adjustments in flowering time is of paramount importance both in wild ecosystems and in agriculture. As global climate patterns shift, a deeper understanding of FT’s regulation will be indispensable for crop improvement and sustainable agriculture. Moreover, the FT paradigm provides a model for studying mobile signals in multicellular organisms, and careful GO annotation of FT will facilitate comparative genomics studies that extend these insights to other organisms (narayan2019analysisofthe pages 11-15, pin2012themultifacetedroles pages 2-3).

In conclusion, a comprehensive view of FT underscores its role as a central, multifaceted regulator of flowering time. Its function, cellular dynamics, and evolutionary history not only exemplify the elegant integration of environmental signals with developmental processes but also provide critical parameters for annotating gene function within the Gene Ontology framework. Continued interdisciplinary research on FT will remain essential for updating and refining genomic databases, ensuring that the annotations accurately reflect the complex biology of flowering (golembeski2015photoperiodicregulationof pages 10-11, komeda2004geneticregulationof pages 6-8).

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This report, synthesized from multiple studies in Arabidopsis thaliana (narayan2019analysisofthe pages 11-15, pin2012themultifacetedroles pages 2-3, takagi2023photoperiodicfloweringin pages 13-14, golembeski2015photoperiodicregulationof pages 10-11, komeda2004geneticregulationof pages 6-8, lebedeva2020theevolutionaryaspects pages 1-2, mathieu2007exportofft pages 1-2, matsoukas2015florigensandantiflorigens pages 3-5, narayan2019analysisofthe pages 15-19, pin2012themultifacetedroles pages 1-2, pin2012themultifacetedroles pages 3-7, wigge2011ftamobile pages 2-3, wickland2015thefloweringlocus pages 15-16, wickland2015thefloweringlocus pages 6-9), offers a detailed analysis of FT’s functions, localization, biological roles, structural properties, regulatory mechanisms, and evolutionary conservation. This integrated knowledge base provides crucial support for the precise GO annotation of FT, ensuring that its description encapsulates its central role as a mobile floral signal in regulating the transition from vegetative growth to flowering in Arabidopsis thaliana.

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End of Report

All key information is supported by the indicated citations in the normal flow of the text.

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(pin2012themultifacetedroles pages 14-14): P. A. PIN and O. NILSSON. The multifaceted roles of flowering locus t in plant development. Plant, cell & environment, 35 10:1742-55, Oct 2012. URL: https://doi.org/10.1111/j.1365-3040.2012.02558.x, doi:10.1111/j.1365-3040.2012.02558.x. This article has 403 citations.
(wigge2011ftamobile pages 1-2): Philip A. Wigge. Ft, a mobile developmental signal in plants. Current Biology, 21:R374-R378, May 2011. URL: https://doi.org/10.1016/j.cub.2011.03.038, doi:10.1016/j.cub.2011.03.038. This article has 189 citations and is from a highest quality peer-reviewed journal.
(putterill2016ftandflorigen pages 4-5): Joanna Putterill and Erika Varkonyi-Gasic. Ft and florigen long-distance flowering control in plants. Current opinion in plant biology, 33:77-82, Oct 2016. URL: https://doi.org/10.1016/j.pbi.2016.06.008, doi:10.1016/j.pbi.2016.06.008. This article has 188 citations and is from a peer-reviewed journal.
(putterill2016ftandflorigen pages 1-2): Joanna Putterill and Erika Varkonyi-Gasic. Ft and florigen long-distance flowering control in plants. Current opinion in plant biology, 33:77-82, Oct 2016. URL: https://doi.org/10.1016/j.pbi.2016.06.008, doi:10.1016/j.pbi.2016.06.008. This article has 188 citations and is from a peer-reviewed journal.
(wickland2015thefloweringlocus pages 15-16): Daniel P. Wickland and Yoshie Hanzawa. The flowering locus t/terminal flower 1 gene family: functional evolution and molecular mechanisms. Molecular plant, 8 7:983-97, Jul 2015. URL: https://doi.org/10.1016/j.molp.2015.01.007, doi:10.1016/j.molp.2015.01.007. This article has 446 citations and is from a highest quality peer-reviewed journal.
(wickland2015thefloweringlocus pages 6-9): Daniel P. Wickland and Yoshie Hanzawa. The flowering locus t/terminal flower 1 gene family: functional evolution and molecular mechanisms. Molecular plant, 8 7:983-97, Jul 2015. URL: https://doi.org/10.1016/j.molp.2015.01.007, doi:10.1016/j.molp.2015.01.007. This article has 446 citations and is from a highest quality peer-reviewed journal.
(turck2008regulationandidentity pages 8-9): Franziska Turck, Fabio Fornara, and George Coupland. Regulation and identity of florigen: flowering locus t moves center stage. Annual Review of Plant Biology, 59:573-594, Jun 2008. URL: https://doi.org/10.1146/annurev.arplant.59.032607.092755, doi:10.1146/annurev.arplant.59.032607.092755. This article has 1217 citations and is from a domain leading peer-reviewed journal.
(wickland2015thefloweringlocus pages 9-12): Daniel P. Wickland and Yoshie Hanzawa. The flowering locus t/terminal flower 1 gene family: functional evolution and molecular mechanisms. Molecular plant, 8 7:983-97, Jul 2015. URL: https://doi.org/10.1016/j.molp.2015.01.007, doi:10.1016/j.molp.2015.01.007. This article has 446 citations and is from a highest quality peer-reviewed journal.
(prewitt2021interspeciesfunctionalcompatibility pages 1-2): S. F. Prewitt, A. Shalit-Kaneh, S. N. Maximova, and M. J. Guiltinan. Inter-species functional compatibility of the theobroma cacao and arabidopsis ft orthologs: 90 million years of functional conservation of meristem identity genes. BMC Plant Biology, May 2021. URL: https://doi.org/10.1186/s12870-021-02982-y, doi:10.1186/s12870-021-02982-y. This article has 7 citations and is from a peer-reviewed journal.
(narayan2019analysisofthe pages 81-85): Om Narayan. Analysis of the bzip transcription factor fdp and its interaction with floral regulators in arabidopsis thaliana. ArXiv, Feb 2019. URL: https://doi.org/10.15496/publikation-27683, doi:10.15496/publikation-27683. This article has 0 citations.
(pin2012themultifacetedroles pages 1-2): P. A. PIN and O. NILSSON. The multifaceted roles of flowering locus t in plant development. Plant, cell & environment, 35 10:1742-55, Oct 2012. URL: https://doi.org/10.1111/j.1365-3040.2012.02558.x, doi:10.1111/j.1365-3040.2012.02558.x. This article has 403 citations.

📄 View Raw YAML

id: Q9SXZ2
gene_symbol: FT
taxon:
  id: NCBITaxon:3702
  label: Arabidopsis thaliana
description: FT encodes a 20-kDa protein belonging to the 
  phosphatidylethanolamine-binding protein (PEBP) family that functions as the 
  mobile floral stimulus (florigen) in Arabidopsis thaliana. FT integrates 
  environmental cues—particularly long-day photoperiods and temperature 
  signals—with endogenous timing mechanisms to orchestrate the transition from 
  vegetative to reproductive growth. The protein is synthesized in the leaf 
  cytoplasm, specifically in phloem companion cells, following transcriptional 
  activation by CONSTANS (CO) under long-day conditions. After synthesis, FT is 
  actively loaded into sieve tube elements and transported via the phloem 
  vascular system to the shoot apical meristem (SAM). At the SAM, FT is imported
  into the nucleus where it interacts with bZIP transcription factors FD/BZIP14 
  and FDP/BZIP27 to form the florigen activation complex (FAC). The FAC binds to
  promoters of floral meristem identity genes including APETALA1 (AP1), 
  FRUITFULL (FUL), and SEPALLATA3 (SEP3), ultimately committing the meristem to 
  flower formation. FT also interacts with regulatory proteins including 
  FTIP1/MCTP1 (which facilitates phloem transport), 14-3-3 adaptor proteins 
  (which mediate nuclear import), and NAKR1 (which modulates subcellular 
  trafficking). The protein undergoes proteasome-dependent degradation for tight
  regulation and is subject to chromatin-level control through histone 
  modifications at its locus. This non-cell-autonomous signaling mechanism 
  ensures synchrony between environmental response and developmental 
  decision-making, making FT a critical molecular integrator in flowering time 
  control.
existing_annotations:
  - term:
      id: GO:0005634
      label: nucleus
    evidence_type: IEA
    original_reference_id: GO_REF:0000044
    review:
      summary: FT is transported to the nucleus at the shoot apical meristem 
        where it interacts with bZIP transcription factors to activate floral 
        meristem identity genes. Nuclear localization is essential for its 
        function.
      action: ACCEPT
      supported_by:
        - reference_id: file:ARATH/FT/FT-deep-research-perplexity-lite.md
          supporting_text: See deep research file for comprehensive analysis
  - term:
      id: GO:0005737
      label: cytoplasm
    evidence_type: IEA
    original_reference_id: GO_REF:0000044
    review:
      summary: FT is synthesized in the leaf cytoplasm, particularly in phloem 
        companion cells, before being transported to the shoot apical meristem. 
        UniProt confirms cytoplasmic localization.
      action: ACCEPT
  - term:
      id: GO:0005783
      label: endoplasmic reticulum
    evidence_type: IEA
    original_reference_id: GO_REF:0000044
    review:
      summary: UniProt curates an endoplasmic reticulum location for FT
        (PubMed:22529749), but this reflects transport-machinery association
        rather than a site where FT carries out its florigen function. Falcon
        deep research describes the FT-interacting protein FTIP1 as an ER
        membrane protein mediating companion-cell-to-sieve-element movement via
        a continuous ER network, so the ER signal is best interpreted as part
        of the trafficking route, not a functional compartment. FT acts
        functionally in the cytoplasm and nucleus. Retained but flagged as an
        over-annotation rather than removed, since the curated location is real.
      action: MARK_AS_OVER_ANNOTATED
      supported_by:
        - reference_id: file:ARATH/FT/FT-deep-research-falcon.md
          supporting_text: |-
            **FTIP1**: an ER membrane protein implicated in CC→SE movement via
            a continuous ER network across plasmodesmata.
  - term:
      id: GO:0009908
      label: flower development
    evidence_type: IEA
    original_reference_id: GO_REF:0000043
    review:
      summary: FT promotes the transition from vegetative to reproductive 
        development and is essential for flower development. It activates floral
        meristem identity genes at the shoot apical meristem.
      action: ACCEPT
  - term:
      id: GO:0030154
      label: cell differentiation
    evidence_type: IEA
    original_reference_id: GO_REF:0000043
    review:
      summary: This term is too broad and non-specific for FT function. It
        derives from a UniProt keyword mapping (GO_REF:0000043). FT has a
        specific role in flowering time control and floral meristem identity
        rather than general cell differentiation; the generic parent term
        over-annotates the gene. Falcon deep research frames FT as a mobile
        signaling protein/transcriptional co-regulator that promotes the
        vegetative-to-reproductive phase transition, not a general
        differentiation factor.
      action: MARK_AS_OVER_ANNOTATED
      supported_by:
        - reference_id: file:ARATH/FT/FT-deep-research-falcon.md
          supporting_text: |-
            FT is **not an enzyme** and does not catalyze a chemical reaction.
            Instead, it functions as a **mobile signaling
            protein/transcriptional co-regulator** that promotes flowering by
            forming protein complexes at the SAM with DNA-binding transcription
            factors.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:16099979
    review:
      summary: FT interacts with FD bZIP transcription factors, which is crucial
        for its function. However, this generic protein binding term is not 
        informative about specific function.
      action: REMOVE
      supported_by:
        - reference_id: PMID:16099979
          supporting_text: FD, a bZIP protein mediating signals from the floral 
            pathway integrator FT at the shoot apex.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:17189287
    review:
      summary: Generic protein binding term lacks specificity about FT molecular
        function. More specific terms better describe its activities.
      action: REMOVE
      supported_by:
        - reference_id: PMID:17189287
          supporting_text: Dec 22. Molecular basis of late-flowering phenotype 
            caused by dominant epi-alleles of the FWA locus in Arabidopsis.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:19656342
    review:
      summary: Non-specific protein binding term does not capture FT specific 
        molecular function as florigen and PEBP family member.
      action: REMOVE
      supported_by:
        - reference_id: PMID:19656342
          supporting_text: 2009 Jul 25. Genetic and spatial interactions between
            FT, TSF and SVP during the early stages of floral induction in 
            Arabidopsis.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:29259105
    review:
      summary: Generic protein binding annotation lacks specificity about FT 
        molecular function. Remove in favor of more specific terms.
      action: REMOVE
      supported_by:
        - reference_id: PMID:29259105
          supporting_text: Dec 19. Characterization of Multiple C2 Domain and 
            Transmembrane Region Proteins in Arabidopsis.
  - term:
      id: GO:0010022
      label: meristem determinacy
    evidence_type: IGI
    original_reference_id: PMID:30943325
    review:
      summary: FT plays a role in determining inflorescence meristem identity 
        and fate. Genetic interaction studies show FT antagonizes TFL1 in 
        meristem determinacy control.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:30943325
          supporting_text: Genetic interactions reveal the antagonistic roles of
            FT/TSF and TFL1 in the determination of inflorescence meristem
            identity in Arabidopsis.
        - reference_id: file:ARATH/FT/FT-deep-research-falcon.md
          supporting_text: |-
            The antagonistic PEBP-family member **TFL1** is described as
            opposing FT function at shared FD-bound targets, effectively tuning
            floral induction by competition at the SAM.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:22529749
    review:
      summary: Generic protein binding term is not informative about FT specific
        function as mobile flowering signal.
      action: REMOVE
      supported_by:
        - reference_id: PMID:22529749
          supporting_text: Apr 17. FTIP1 is an essential regulator required for 
            florigen transport.
  - term:
      id: GO:0010119
      label: regulation of stomatal movement
    evidence_type: IMP
    original_reference_id: PMID:21737277
    review:
      summary: This appears to be a peripheral function not central to FT role 
        as florigen. FT primary function is flowering time control, not stomatal
        regulation.
      action: KEEP_AS_NON_CORE
      supported_by:
        - reference_id: PMID:21737277
          supporting_text: 2011 Jul 7. FLOWERING LOCUS T regulates stomatal 
            opening.
  - term:
      id: GO:0009909
      label: regulation of flower development
    evidence_type: IGI
    original_reference_id: PMID:20626659
    review:
      summary: FT regulates flower development by promoting floral meristem fate
        and determinacy. This is a core function of FT as the mobile flowering 
        signal.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:20626659
          supporting_text: Arabidopsis BLADE-ON-PETIOLE1 and 2 promote floral 
            meristem fate and determinacy in a previously undefined pathway 
            targeting APETALA1 and AGAMOUS-LIKE24.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:16099980
    review:
      summary: Non-specific protein binding term does not describe FT specific 
        molecular activities. More specific molecular function terms are 
        preferred.
      action: REMOVE
      supported_by:
        - reference_id: PMID:16099980
          supporting_text: Integration of spatial and temporal information 
            during floral induction in Arabidopsis.
  - term:
      id: GO:0005634
      label: nucleus
    evidence_type: IDA
    original_reference_id: PMID:16099979
    review:
      summary: Experimental evidence confirms FT nuclear localization at the 
        shoot apical meristem where it interacts with FD transcription factors. 
        This is essential for function.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:16099979
          supporting_text: FD, a bZIP protein mediating signals from the floral 
            pathway integrator FT at the shoot apex.
  - term:
      id: GO:0005737
      label: cytoplasm
    evidence_type: IDA
    original_reference_id: PMID:16099979
    review:
      summary: Experimental evidence confirms FT cytoplasmic localization. FT is
        synthesized in leaf cytoplasm before transport to the shoot apical 
        meristem.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:16099979
          supporting_text: FD, a bZIP protein mediating signals from the floral 
            pathway integrator FT at the shoot apex.
  - term:
      id: GO:0048573
      label: photoperiodism, flowering
    evidence_type: IEP
    original_reference_id: PMID:17446353
    review:
      summary: FT is a key component of the photoperiodic flowering pathway. It 
        integrates long-day photoperiod signals and promotes flowering. This is 
        a core function of FT.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:17446353
          supporting_text: Apr 19. FT protein movement contributes to
            long-distance signaling in floral induction of Arabidopsis.
        - reference_id: file:ARATH/FT/FT-deep-research-falcon.md
          supporting_text: |-
            CO directly activates **FT** transcription in leaves; FT is the key
            floral pathway integrator under long days
        - reference_id: file:ARATH/FT/FT-deep-research-falcon.md
          supporting_text: |-
            FT expression is activated in leaf **phloem companion cells (CCs)**
            under inductive conditions (notably long days), and the **FT
            protein is loaded into sieve elements (SEs)** for phloem transport.
  - term:
      id: GO:0008429
      label: phosphatidylethanolamine binding
    evidence_type: ISS
    original_reference_id: PMID:10583961
    review:
      summary: FT belongs to the PEBP (phosphatidylethanolamine-binding protein)
        family. This molecular function is characteristic of the protein family 
        and represents its biochemical activity.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:10583961
          supporting_text: Activation tagging of the floral inducer FT.
        - reference_id: file:ARATH/FT/FT-deep-research-falcon.md
          supporting_text: |-
            Reviews emphasize that PEBP-family proteins such as FT do **not
            bind DNA directly**, but act through interaction with
            transcriptional regulators such as bZIP factors in the FD class.
  - term:
      id: GO:0009911
      label: positive regulation of flower development
    evidence_type: IMP
    original_reference_id: PMID:10583960
    review:
      summary: This is the core function of FT. It acts as the mobile floral 
        stimulus (florigen) that promotes flowering by activating floral 
        meristem identity genes. Strong experimental support.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:10583960
          supporting_text: A pair of related genes with antagonistic roles in
            mediating flowering signals.
        - reference_id: file:ARATH/FT/FT-deep-research-falcon.md
          supporting_text: |-
            In *Arabidopsis*, **FT encodes a mobile protein signal** produced
            in leaves that is transported to the SAM, where it triggers the
            vegetative-to-reproductive phase transition.
  - term:
      id: GO:0009911
      label: positive regulation of flower development
    evidence_type: IMP
    original_reference_id: PMID:10583961
    review:
      summary: Core function of FT as florigen. Promotes transition from 
        vegetative to reproductive development by activating floral meristem 
        identity genes. Experimental evidence confirms this essential role.
      action: ACCEPT
      supported_by:
        - reference_id: PMID:10583961
          supporting_text: Activation tagging of the floral inducer FT.
        - reference_id: file:ARATH/FT/FT-deep-research-falcon.md
          supporting_text: |-
            FT is **not an enzyme** and does not catalyze a chemical reaction.
            Instead, it functions as a **mobile signaling
            protein/transcriptional co-regulator** that promotes flowering by
            forming protein complexes at the SAM with DNA-binding transcription
            factors.
  - term:
      id: GO:0140297
      label: DNA-binding transcription factor binding
    evidence_type: IPI
    original_reference_id: PMID:16099979
    review:
      summary: >-
        NEW annotation. FT directly interacts with the bZIP DNA-binding
        transcription factors FD/BZIP14 and FDP/BZIP27 at the shoot apical
        meristem (PMID:16099979, PMID:16099980). This informative molecular
        function replaces the generic GO:0005515 'protein binding' annotations
        and captures the specific partner class through which FT, which does
        not bind DNA itself, acts.
      action: NEW
      supported_by:
        - reference_id: PMID:16099979
          supporting_text: FD, a bZIP protein mediating signals from the floral
            pathway integrator FT at the shoot apex.
        - reference_id: file:ARATH/FT/FT-deep-research-falcon.md
          supporting_text: |-
            Reviews emphasize that PEBP-family proteins such as FT do **not
            bind DNA directly**, but act through interaction with
            transcriptional regulators such as bZIP factors in the FD class.
  - term:
      id: GO:0003713
      label: transcription coactivator activity
    evidence_type: IPI
    original_reference_id: PMID:16099980
    review:
      summary: >-
        NEW annotation. As the mobile florigen, FT acts as a transcriptional
        co-regulator: it does not bind DNA directly but, within the florigen
        activation complex (FT + FD-class bZIPs + 14-3-3), promotes
        transcriptional activation of floral meristem identity genes such as
        AP1 at the shoot apical meristem (PMID:16099979, PMID:16099980). This
        informative molecular function captures FT's positive role in
        target-gene activation that the generic 'protein binding' terms missed.
        Evidence code is IPI: GO:0003713 is a molecular function (so IMP is
        inappropriate), and the coactivator activity is established through
        FT's physical interaction with the DNA-binding bZIP factor FD that is
        required to activate AP1 (consistent with the GO definition: activation
        "via binding to a DNA-binding transcription factor").
      action: NEW
      supported_by:
        - reference_id: PMID:16099980
          supporting_text: A complex of FT and FD proteins in turn can activate
            floral identity genes such as APETALA1 (AP1).
        - reference_id: file:ARATH/FT/FT-deep-research-falcon.md
          supporting_text: |-
            FT is **not an enzyme** and does not catalyze a chemical reaction.
            Instead, it functions as a **mobile signaling
            protein/transcriptional co-regulator** that promotes flowering by
            forming protein complexes at the SAM with DNA-binding transcription
            factors.
references:
  - id: GO_REF:0000043
    title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword
      mapping
    findings:
      - statement: "Electronic GO annotation derived from mapping of UniProtKB/Swiss-Prot keywords (e.g. flowering-related keywords) to GO terms for FT; supports generic process-level annotations."
  - id: GO_REF:0000044
    title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular
      Location vocabulary mapping, accompanied by conservative changes to GO
      terms applied by UniProt.
    findings:
      - statement: "Electronic GO annotation derived from UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping; FT is annotated to cytoplasm and nucleus consistent with a mobile florigen carrying both leaf-source cytoplasmic and SAM-nuclear pools."
  - id: PMID:10583960
    title: A pair of related genes with antagonistic roles in mediating
      flowering signals.
    findings:
      - statement: "FT promotes flowering and is positively regulated by CONSTANS (CO) in the long-day photoperiodic pathway; loss of FT delays flowering and overexpression causes precocious, CO/photoperiod-independent flowering."
        supporting_text: "FT, together with LFY, promotes flowering and is positively regulated by CO. Loss of FT causes delay in flowering, whereas overexpression of FT results in precocious flowering independent of CO or photoperiod."
        reference_section_type: ABSTRACT
      - statement: "FT acts in part downstream of CO and mediates flowering signals antagonistically with its paralog TERMINAL FLOWER1 (TFL1), establishing the FT/TFL1 antagonism that tunes the floral transition."
        supporting_text: "FT acts in part downstream of CO and mediates signals for flowering in an antagonistic manner with its homologous gene, TERMINAL FLOWER1 (TFL1)."
        reference_section_type: ABSTRACT
  - id: PMID:10583961
    title: Activation tagging of the floral inducer FT.
    findings:
      - statement: "FT was isolated by activation tagging as a floral inducer acting in parallel with the meristem-identity gene LEAFY (LFY), partially downstream of CONSTANS (CO)."
        supporting_text: "FLOWERING LOCUS T (FT), which acts in parallel with the meristem-identity gene LEAFY (LFY) to induce flowering of Arabidopsis, was isolated by activation tagging. Like LFY, FT acts partially downstream of CONSTANS (CO), which promotes flowering in response to long days."
        reference_section_type: ABSTRACT
      - statement: "The deduced FT protein sequence is similar to TERMINAL FLOWER1 (an inhibitor of flowering) and to membrane-associated mammalian PEBP-family proteins; FT does not directly control transcription or transcript processing, foreshadowing its role as a non-DNA-binding signaling protein."
        supporting_text: "Unlike many other floral regulators, the deduced sequence of the FT protein does not suggest that it directly controls transcription or transcript processing. Instead, it is similar to the sequence of TERMINAL FLOWER 1 (TFL1), an inhibitor of flowering that also shares sequence similarity with membrane-associated mammalian proteins."
        reference_section_type: ABSTRACT
  - id: PMID:16099979
    title: FD, a bZIP protein mediating signals from the floral pathway
      integrator FT at the shoot apex.
    findings:
      - statement: "FT and the bZIP transcription factor FD are interdependent partners (via protein interaction) that act together at the shoot apex to promote floral transition, providing the molecular basis for FT's transcription-coactivator role."
        supporting_text: "FD and FT are interdependent partners through protein interaction and act at the shoot apex to promote floral transition and to initiate floral development through transcriptional activation of a floral meristem identity gene, APETALA1 (AP1)."
        reference_section_type: ABSTRACT
      - statement: "The FT/FD complex transcriptionally activates APETALA1 (AP1), a floral meristem-identity gene, providing direct support for FT involvement in positive regulation of flower development."
        supporting_text: "FD and FT are interdependent partners through protein interaction and act at the shoot apex to promote floral transition and to initiate floral development through transcriptional activation of a floral meristem identity gene, APETALA1 (AP1)."
        reference_section_type: ABSTRACT
      - statement: "FT mRNA is expressed in the vasculature of cotyledons and leaves, while FD is preferentially expressed in the shoot apex, consistent with FT being a leaf-derived long-distance signal that meets its bZIP partner at the apex."
        supporting_text: "FLOWERING LOCUS T (FT) is a conserved promoter of flowering that acts downstream of various regulatory pathways, including one that mediates photoperiodic induction through CONSTANS (CO), and is expressed in the vasculature of cotyledons and leaves. A bZIP transcription factor, FD, preferentially expressed in the shoot apex is required for FT to promote flowering."
        reference_section_type: ABSTRACT
  - id: PMID:16099980
    title: Integration of spatial and temporal information during floral
      induction in Arabidopsis.
    findings:
      - statement: "A primary response to floral induction is activation of FT RNA expression in leaves; because flowers form at the distant shoot apex, FT (a small, possibly mobile protein) integrates temporal information for flowering."
        supporting_text: "A primary response to floral induction is the activation of FT RNA expression in leaves. Because flowers form at a distant site, the shoot apex, these data suggest that FT primarily controls the timing of flowering."
        reference_section_type: ABSTRACT
      - statement: "A complex of FT and FD proteins activates floral identity genes such as APETALA1 (AP1), confirming the FT-FD activation module mediates floral meristem identity transcription."
        supporting_text: "A complex of FT and FD proteins in turn can activate floral identity genes such as APETALA1 (AP1)."
        reference_section_type: ABSTRACT
  - id: PMID:17189287
    title: Molecular basis of late-flowering phenotype caused by dominant
      epi-alleles of the FWA locus in Arabidopsis.
    findings:
      - statement: "Ectopic FWA blocks the flowering pathway at or downstream of FT, with FWA binding to FT (yeast two-hybrid and pull-down) suggesting FWA delays flowering by interfering with FT/FD complex formation."
        supporting_text: "The previous reports that fwa suppressed the precocious-flowering phenotype of plants overexpressing FLOWERING LOCUS T (FT) suggest that the flowering pathway(s) either at and/or downstream of FT is blocked by FWA."
        reference_section_type: ABSTRACT
  - id: PMID:17446353
    title: FT protein movement contributes to long-distance signaling in floral
      induction of Arabidopsis.
    findings:
      - statement: "FT mRNA is required only transiently in the leaf; FT fusion proteins expressed specifically in phloem cells move to the apex and across grafts, providing direct evidence that FT protein acts as a long-distance (florigenic) signal."
        supporting_text: "We found that FT messenger RNA is required only transiently in the leaf. In addition, FT fusion proteins expressed specifically in phloem cells move to the apex and move long distances between grafted plants."
        reference_section_type: ABSTRACT
      - statement: "FT does not activate an intermediate messenger in leaves; therefore FT protein itself constitutes the long-distance signal that induces Arabidopsis flowering."
        supporting_text: "we provide evidence that FT does not activate an intermediate messenger in leaves. We conclude that FT protein acts as a long-distance signal that induces Arabidopsis flowering."
        reference_section_type: ABSTRACT
  - id: PMID:19656342
    title: Genetic and spatial interactions between FT, TSF and SVP during the
      early stages of floral induction in Arabidopsis.
    findings:
      - statement: "FT and its paralog TSF redundantly mediate photoperiodic flowering; the ft tsf double mutant is photoperiod-insensitive and fully suppresses the early-flowering phenotype of CO overexpression."
        supporting_text: "we show that FT and the closely related TSF are not essential for flowering, but that the double mutant is photoperiod-insensitive. Inactivation of both genes also fully suppresses the early-flowering phenotype caused by over-expression of constans (CO), a transcriptional regulator in the photoperiod pathway."
        reference_section_type: ABSTRACT
      - statement: "FT and TSF interact with the same bZIP transcription factors (FD/FDP-class) in yeast, demonstrating shared biochemical function as transcription-coactivator partners of bZIPs."
        supporting_text: "we demonstrate that TSF and FT have similar biochemical functions by showing that they interact in yeast with the same bZIP transcription factors."
        reference_section_type: ABSTRACT
      - statement: "Phloem-companion-cell-specific FT or TSF expression rescues flowering in ft tsf double mutants, demonstrating that FT need not be expressed in the meristem and is loaded into the phloem from companion cells."
        supporting_text: "Expression of FT or TSF from promoters specific for phloem companion cells drives early flowering of the double mutant, so no expression of either gene is required in the meristem."
        reference_section_type: ABSTRACT
      - statement: "FT and TSF are repressed by the MADS-box transcription factor SVP, integrating SVP repression into the FT/TSF photoperiodic flowering pathway."
        supporting_text: "TSF, like FT, is repressed by SVP"
        reference_section_type: ABSTRACT
  - id: PMID:20626659
    title: Arabidopsis BLADE-ON-PETIOLE1 and 2 promote floral meristem fate and
      determinacy in a previously undefined pathway targeting APETALA1 and
      AGAMOUS-LIKE24.
    findings:
      - statement: "BOP1/2 promote floral meristem identity by upregulating APETALA1 via direct interactions with TGA bZIP transcription factors at the AP1 promoter, defining a parallel pathway to FT/FD that converges on AP1."
        supporting_text: "BOP1/2 are recruited to the promoter of AP1 through direct interactions with TGA bZIP transcription factors"
        reference_section_type: ABSTRACT
      - statement: "BOP1/2, LFY and AP1 converge to down-regulate flowering-time regulators including AGAMOUS-LIKE24 in stage 2 floral meristems, providing context for how the FT/FD-AP1 pathway is fine-tuned by parallel inputs."
        supporting_text: "all three activities converge to down-regulate flowering-time regulators including AGAMOUS-LIKE24 in stage 2 floral meristems"
        reference_section_type: ABSTRACT
  - id: PMID:21737277
    title: FLOWERING LOCUS T regulates stomatal opening.
    findings:
      - statement: "FT is expressed in guard cells and regulates stomatal opening downstream of phototropin (phot1/phot2) blue-light signaling, indicating an additional, non-floral role for FT in guard cells."
        supporting_text: "FLOWERING LOCUS T (FT) is expressed in guard cells and regulates stomatal opening."
        reference_section_type: ABSTRACT
      - statement: "The scs1-1 (elf3 phot1 phot2) suppressor shows open stomata with high H+-ATPase activity, linking FT/ELF3 to guard-cell H+-ATPase activation; supports an annotation of FT to stomatal-opening regulation as a non-core/clock-output role."
        supporting_text: "scs1-1 (elf3 phot1 phot2 triple mutant) had an open-stomata phenotype with high H(+)-ATPase activity"
        reference_section_type: ABSTRACT
  - id: PMID:22529749
    title: FTIP1 is an essential regulator required for florigen transport.
    findings:
      - statement: "FT-INTERACTING PROTEIN 1 (FTIP1), an ER membrane protein, is essential for FT protein transport to the shoot apex in Arabidopsis; loss of FTIP1 causes late flowering under long days partly via compromised FT movement, establishing that florigen transport is a regulated process."
        supporting_text: "FT-INTERACTING PROTEIN 1 (FTIP1), is an essential regulator required for FT protein transport in Arabidopsis. Loss of function of FTIP1 exhibits late flowering under long days, which is partly due to the compromised FT movement to the shoot apex."
        reference_section_type: ABSTRACT
      - statement: "FTIP1 and FT share similar mRNA expression patterns and subcellular localization and interact directly, indicating an active loading/trafficking mechanism for FT in phloem companion cells."
        supporting_text: "FTIP1 and FT share similar mRNA expression patterns and subcellular localization, and they interact"
        reference_section_type: ABSTRACT
  - id: PMID:29259105
    title: Characterization of Multiple C2 Domain and Transmembrane Region
      Proteins in Arabidopsis.
    findings:
      - statement: "Systematic characterization of the 16-member Arabidopsis MCTP family confirms that MCTP1 (FTIP1) C2 domains cooperate to regulate FTIP1's role in FT-dependent flowering-time control, supporting the regulated trafficking of FT."
        supporting_text: "We further analyze in vivo effects of three C2 domains on the regulatory role of MCTP1 (FTIP1) in flowering time control in Arabidopsis, demonstrating that these C2 domains may be cooperative to mediate FTIP1 function during the floral transition."
        reference_section_type: ABSTRACT
  - id: PMID:30943325
    title: Genetic interactions reveal the antagonistic roles of FT/TSF and TFL1
      in the determination of inflorescence meristem identity in Arabidopsis.
    findings:
      - statement: "FT/TSF and TFL1 act antagonistically in inflorescence meristem identity: ft tsf mutants generate a hyper-vegetative shoot (like TFL1 overexpression) while FT or TSF overexpression generates a terminal flower (like tfl1 mutants), placing FT in inflorescence-meristem identity control."
        supporting_text: "The ft-10 tsf-1 mutants produced a compact inflorescence surrounded by serrated leaves (hyper-vegetative shoot) at the early bolting stage, as did plants overexpressing TFL1. Plants overexpressing FT or TSF (or both FT and TFL1) generated a terminal flower, as did tfl1-20 mutants."
        reference_section_type: ABSTRACT
      - statement: "Grafting demonstrates that long-distance FT signal from a 35S::FT rootstock restores normal inflorescence patterning to ft tsf scions, confirming FT functions as a mobile florigen in inflorescence meristem identity."
        supporting_text: "Grafting ft-10 tsf-1 or ft-10 tsf-1 tfl1-20 mutant scions to 35S::FT rootstock plants produced a normal inflorescence and a terminal flower in the scion plants, respectively"
        reference_section_type: ABSTRACT
  - id: file:ARATH/FT/FT-deep-research-perplexity-lite.md
    title: Deep research on FT function
    findings:
      - statement: "Synthesis of the FT literature - FT is a leaf-produced mobile floral stimulus (florigen) that, after long-distance transport through the phloem, partners with FD-class bZIP transcription factors at the shoot apex to activate floral meristem-identity genes (AP1, SOC1, LFY)."
  - id: file:ARATH/FT/FT-deep-research-falcon.md
    title: Falcon (Edison Scientific) deep research on Arabidopsis FT (florigen)
      function, transport, and mode of action at the shoot apical meristem
    findings:
      - reference_section_type: OTHER
        supporting_text: |-
          In *Arabidopsis*, **FT encodes a mobile protein signal** produced in
          leaves that is transported to the SAM, where it triggers the
          vegetative-to-reproductive phase transition.
      - reference_section_type: OTHER
        supporting_text: |-
          FT is **not an enzyme** and does not catalyze a chemical reaction.
          Instead, it functions as a **mobile signaling
          protein/transcriptional co-regulator** that promotes flowering by
          forming protein complexes at the SAM with DNA-binding transcription
          factors.
      - reference_section_type: OTHER
        supporting_text: |-
          Reviews emphasize that PEBP-family proteins such as FT do **not bind
          DNA directly**, but act through interaction with transcriptional
          regulators such as bZIP factors in the FD class.
      - reference_section_type: OTHER
        supporting_text: |-
          FT expression is activated in leaf **phloem companion cells (CCs)**
          under inductive conditions (notably long days), and the **FT protein
          is loaded into sieve elements (SEs)** for phloem transport.
      - reference_section_type: OTHER
        supporting_text: |-
          Once in the SEs, FT traffics through the **phloem stream** to the
          shoot. This movement is considered regulated, not a simple diffusion
          process.
      - reference_section_type: OTHER
        supporting_text: |-
          At the **shoot apical meristem**, FT participates in complexes that
          reprogram gene expression toward floral fate, including activation of
          floral meristem identity programs.
      - reference_section_type: OTHER
        supporting_text: |-
          The antagonistic PEBP-family member **TFL1** is described as opposing
          FT function at shared FD-bound targets, effectively tuning floral
          induction by competition at the SAM.
      - reference_section_type: OTHER
        supporting_text: |-
          CO directly activates **FT** transcription in leaves; FT is the key
          floral pathway integrator under long days
proposed_new_terms:
  - proposed_name: florigen activation complex assembly
    proposed_definition: The formation of a transcriptional activation complex 
      containing florigen (FT) and bZIP transcription factors that activates 
      floral meristem identity gene expression
    proposed_parent:
      id: GO:0009909
      label: regulation of flower development
    justification: FT forms the florigen activation complex (FAC) with FD/FDP 
      transcription factors, which is essential for activating floral 
      development genes
    supported_by:
      - reference_id: file:ARATH/FT/FT-falcon-research.md
        supporting_text: In the SAM, FT interacts with the bZIP transcription 
          factor FD (and its homolog FDP) to form a complex known as the 
          florigen activation complex (FAC). The FAC then binds to the promoters
          of floral meristem identity genes
  - proposed_name: phloem-mediated long-distance protein transport
    proposed_definition: The process by which proteins synthesized in source 
      tissues are loaded into and transported through the phloem to target 
      tissues for non-cell-autonomous signaling
    proposed_parent:
      id: GO:0015031
      label: protein transport
    justification: FT represents a paradigm for long-distance protein signaling 
      through the phloem vascular system from leaves to the shoot apical 
      meristem
    supported_by:
      - reference_id: file:ARATH/FT/FT-falcon-research.md
        supporting_text: Following synthesis, the mature FT protein is actively 
          loaded into the sieve tube elements of the phloem. This loading 
          process is mediated by interacting proteins such as FTIP1, which are 
          essential for the translocation of FT through the vascular system
core_functions:
  - description: Mobile floral stimulus (florigen) that, at the shoot apical
      meristem, acts as a transcriptional co-regulator within the florigen
      activation complex (FT + FD-class bZIP factors + 14-3-3 proteins) to
      activate floral meristem identity genes and promote flowering. FT itself
      does not bind DNA but enables target-gene activation through its bZIP
      partners.
    molecular_function:
      id: GO:0003713
      label: transcription coactivator activity
    directly_involved_in:
      - id: GO:0009911
        label: positive regulation of flower development
    locations:
      - id: GO:0005634
        label: nucleus
    supported_by:
      - reference_id: file:ARATH/FT/FT-deep-research-falcon.md
        supporting_text: |-
          FT is **not an enzyme** and does not catalyze a chemical reaction.
          Instead, it functions as a **mobile signaling
          protein/transcriptional co-regulator** that promotes flowering by
          forming protein complexes at the SAM with DNA-binding transcription
          factors.
      - reference_id: file:ARATH/FT/FT-deep-research-falcon.md
        supporting_text: |-
          Reviews emphasize that PEBP-family proteins such as FT do **not bind
          DNA directly**, but act through interaction with transcriptional
          regulators such as bZIP factors in the FD class.
  - description: Binds the FD/FDP bZIP DNA-binding transcription factors (and
      redundant partners such as AREB3) at the shoot apical meristem,
      recruiting them into the florigen activation complex that reprograms gene
      expression toward floral fate.
    molecular_function:
      id: GO:0140297
      label: DNA-binding transcription factor binding
    directly_involved_in:
      - id: GO:0010022
        label: meristem determinacy
    locations:
      - id: GO:0005634
        label: nucleus
    supported_by:
      - reference_id: file:ARATH/FT/FT-deep-research-falcon.md
        supporting_text: |-
          At the **shoot apical meristem**, FT participates in complexes that
          reprogram gene expression toward floral fate, including activation of
          floral meristem identity programs.
  - description: Phosphatidylethanolamine-binding protein (PEBP) family member;
      the conserved PEBP/anion-binding fold is the biochemical/structural basis
      that distinguishes the FT activator from the antagonistic TFL1 repressor
      and underlies integration of photoperiodic flowering signals after
      synthesis in leaf phloem companion cells.
    molecular_function:
      id: GO:0008429
      label: phosphatidylethanolamine binding
    directly_involved_in:
      - id: GO:0048573
        label: photoperiodism, flowering
    locations:
      - id: GO:0005737
        label: cytoplasm
    supported_by:
      - reference_id: file:ARATH/FT/FT-deep-research-falcon.md
        supporting_text: |-
          The antagonistic PEBP-family member **TFL1** is described as opposing
          FT function at shared FD-bound targets, effectively tuning floral
          induction by competition at the SAM.
suggested_questions:
  - question: "What is the precise composition and stoichiometry of the florigen activation complex (FT, FD/FDP, 14-3-3 proteins) at native AP1/SOC1 promoters in planta, and how is its assembly regulated by phosphorylation of FD?"
  - question: "How is FT loaded into sieve elements and unloaded at the shoot apical meristem, and which trafficking factors beyond FTIP1 (e.g. other MCTPs, NaKR1) contribute to directional, regulated florigen transport?"
  - question: "Which biochemical feature of the FT PEBP/anion-binding pocket distinguishes activator FT from repressor TFL1 at the same FD-bound cis-elements, and can FT be converted into a TFL1-like repressor (or vice versa) by single-residue swaps in vivo?"
suggested_experiments:
  - description: "In planta FT/FD/14-3-3 complex reconstitution and proximity-labeling (TurboID-FT or TurboID-FD) at the SAM in inductive long-day conditions, with parallel ChIP-seq for FT and FD at AP1/SOC1/LFY loci to map the in vivo florigen activation complex genome-wide."
    hypothesis: "FT/FD/14-3-3 complexes assemble on a defined set of bZIP cis-elements at the SAM and are sufficient to convert vegetative shoot identity into floral meristem identity."
    experiment_type: "Proximity labeling MS + ChIP-seq"
  - description: "Domain-swap and structure-guided point mutagenesis in the FT anion-binding pocket (key residues including Tyr85, Gln140, the external loop) tested in 35S::FT lines for ability to promote vs delay flowering, paired with CRISPR-engineering of equivalent residues in TFL1."
    hypothesis: "A small set of residues in the PEBP anion-binding pocket and external loop determines activator (FT) versus repressor (TFL1) activity at shared FD/bZIP targets, allowing reversible interconversion of florigen and antiflorigen identities."
    experiment_type: "Site-directed mutagenesis with floral transition phenotyping"
  - description: "Live cell imaging of fluorescently tagged FT and FTIP1/MCTP variants in companion-cell/sieve-element regions of the leaf phloem during the floral transition, combined with grafting experiments using rootstocks expressing pCC2::FT-GFP to quantify movement kinetics in different mutants."
    hypothesis: "FTIP1 and additional MCTP-family proteins act sequentially to load FT into sieve elements; loss of specific MCTPs blocks loading without affecting general phloem transport."
    experiment_type: "Live cell imaging with grafting"
status: DRAFT

FT

Gene Description

Proposed New Ontology Terms

florigen activation complex assembly

phloem-mediated long-distance protein transport

Existing Annotations Review

Core Functions

Binds the FD/FDP bZIP DNA-binding transcription factors (and redundant partners such as AREB3) at the shoot apical meristem, recruiting them into the florigen activation complex that reprograms gene expression toward floral fate.

References

Suggested Questions for Experts

Suggested Experiments

Deep Research

Falcon

Research report: Functional annotation of FLOWERING LOCUS T (FT) in Arabidopsis thaliana (UniProt Q9SXZ2, locus At1g65480)

1) Verification of correct gene/protein identity (mandatory disambiguation)

2) Key concepts and current understanding (definitions, mechanism, localization)

2.1 Florigen and FT as a systemic flowering signal

2.2 Primary molecular function of FT (what the protein does)

2.3 Tissue, cellular, and subcellular route: where FT is made and where it acts

2.4 Protein complexes and key interactors: how FT induces flowering at the SAM

3) Recent developments and latest research (prioritized 2023–2024)

3.2 Quantitative transport timing and localization at the SAM

3.3 Expansion of FT-responsive bZIP network at the SAM (primary research)

3.4 Updated understanding of environmental integration upstream of FT

4) Current applications and real-world implementations (2023–2024)

4.1 Flowering-time and architecture engineering via FT/TFL1 editing (quantitative 2024 example)

4.2 Broader flowering-time engineering strategies and expert synthesis (2023)

5) Expert opinions/analysis and open questions

Evidence-backed summary table

Key sources (with URLs and publication dates)

Notes on limitations of this report

Artifacts

Citations

Perplexity

Citations

📚 Additional Documentation

Falcon Research

Falcon Research Report: FT (ARATH)

📄 View Raw YAML

GO Term	Evidence	Action	Reason
GO:0005634 nucleus	IEA GO_REF:0000044	ACCEPT	Summary: FT is transported to the nucleus at the shoot apical meristem where it interacts with bZIP transcription factors to activate floral meristem identity genes. Nuclear localization is essential for its function. Supporting Evidence: file:ARATH/FT/FT-deep-research-perplexity-lite.md See deep research file for comprehensive analysis
GO:0005737 cytoplasm	IEA GO_REF:0000044	ACCEPT	Summary: FT is synthesized in the leaf cytoplasm, particularly in phloem companion cells, before being transported to the shoot apical meristem. UniProt confirms cytoplasmic localization.
GO:0005783 endoplasmic reticulum	IEA GO_REF:0000044	MARK AS OVER ANNOTATED	Summary: UniProt curates an endoplasmic reticulum location for FT (PubMed:22529749), but this reflects transport-machinery association rather than a site where FT carries out its florigen function. Falcon deep research describes the FT-interacting protein FTIP1 as an ER membrane protein mediating companion-cell-to-sieve-element movement via a continuous ER network, so the ER signal is best interpreted as part of the trafficking route, not a functional compartment. FT acts functionally in the cytoplasm and nucleus. Retained but flagged as an over-annotation rather than removed, since the curated location is real. Supporting Evidence: file:ARATH/FT/FT-deep-research-falcon.md FTIP1: an ER membrane protein implicated in CC→SE movement via a continuous ER network across plasmodesmata.
GO:0009908 flower development	IEA GO_REF:0000043	ACCEPT	Summary: FT promotes the transition from vegetative to reproductive development and is essential for flower development. It activates floral meristem identity genes at the shoot apical meristem.
GO:0030154 cell differentiation	IEA GO_REF:0000043	MARK AS OVER ANNOTATED	Summary: This term is too broad and non-specific for FT function. It derives from a UniProt keyword mapping (GO_REF:0000043). FT has a specific role in flowering time control and floral meristem identity rather than general cell differentiation; the generic parent term over-annotates the gene. Falcon deep research frames FT as a mobile signaling protein/transcriptional co-regulator that promotes the vegetative-to-reproductive phase transition, not a general differentiation factor. Supporting Evidence: file:ARATH/FT/FT-deep-research-falcon.md FT is not an enzyme and does not catalyze a chemical reaction. Instead, it functions as a mobile signaling protein/transcriptional co-regulator that promotes flowering by forming protein complexes at the SAM with DNA-binding transcription factors.
GO:0005515 protein binding	IPI PMID:16099979 FD, a bZIP protein mediating signals from the floral pathway...	REMOVE	Summary: FT interacts with FD bZIP transcription factors, which is crucial for its function. However, this generic protein binding term is not informative about specific function. Supporting Evidence: PMID:16099979 FD, a bZIP protein mediating signals from the floral pathway integrator FT at the shoot apex.
GO:0005515 protein binding	IPI PMID:17189287 Molecular basis of late-flowering phenotype caused by domina...	REMOVE	Summary: Generic protein binding term lacks specificity about FT molecular function. More specific terms better describe its activities. Supporting Evidence: PMID:17189287 Dec 22. Molecular basis of late-flowering phenotype caused by dominant epi-alleles of the FWA locus in Arabidopsis.
GO:0005515 protein binding	IPI PMID:19656342 Genetic and spatial interactions between FT, TSF and SVP dur...	REMOVE	Summary: Non-specific protein binding term does not capture FT specific molecular function as florigen and PEBP family member. Supporting Evidence: PMID:19656342 2009 Jul 25. Genetic and spatial interactions between FT, TSF and SVP during the early stages of floral induction in Arabidopsis.
GO:0005515 protein binding	IPI PMID:29259105 Characterization of Multiple C2 Domain and Transmembrane Reg...	REMOVE	Summary: Generic protein binding annotation lacks specificity about FT molecular function. Remove in favor of more specific terms. Supporting Evidence: PMID:29259105 Dec 19. Characterization of Multiple C2 Domain and Transmembrane Region Proteins in Arabidopsis.
GO:0010022 meristem determinacy	IGI PMID:30943325 Genetic interactions reveal the antagonistic roles of FT/TSF...	ACCEPT	Summary: FT plays a role in determining inflorescence meristem identity and fate. Genetic interaction studies show FT antagonizes TFL1 in meristem determinacy control. Supporting Evidence: PMID:30943325 Genetic interactions reveal the antagonistic roles of FT/TSF and TFL1 in the determination of inflorescence meristem identity in Arabidopsis. file:ARATH/FT/FT-deep-research-falcon.md The antagonistic PEBP-family member TFL1 is described as opposing FT function at shared FD-bound targets, effectively tuning floral induction by competition at the SAM.
GO:0005515 protein binding	IPI PMID:22529749 FTIP1 is an essential regulator required for florigen transp...	REMOVE	Summary: Generic protein binding term is not informative about FT specific function as mobile flowering signal. Supporting Evidence: PMID:22529749 Apr 17. FTIP1 is an essential regulator required for florigen transport.
GO:0010119 regulation of stomatal movement	IMP PMID:21737277 FLOWERING LOCUS T regulates stomatal opening.	KEEP AS NON CORE	Summary: This appears to be a peripheral function not central to FT role as florigen. FT primary function is flowering time control, not stomatal regulation. Supporting Evidence: PMID:21737277 2011 Jul 7. FLOWERING LOCUS T regulates stomatal opening.
GO:0009909 regulation of flower development	IGI PMID:20626659 Arabidopsis BLADE-ON-PETIOLE1 and 2 promote floral meristem ...	ACCEPT	Summary: FT regulates flower development by promoting floral meristem fate and determinacy. This is a core function of FT as the mobile flowering signal. Supporting Evidence: PMID:20626659 Arabidopsis BLADE-ON-PETIOLE1 and 2 promote floral meristem fate and determinacy in a previously undefined pathway targeting APETALA1 and AGAMOUS-LIKE24.
GO:0005515 protein binding	IPI PMID:16099980 Integration of spatial and temporal information during flora...	REMOVE	Summary: Non-specific protein binding term does not describe FT specific molecular activities. More specific molecular function terms are preferred. Supporting Evidence: PMID:16099980 Integration of spatial and temporal information during floral induction in Arabidopsis.
GO:0005634 nucleus	IDA PMID:16099979 FD, a bZIP protein mediating signals from the floral pathway...	ACCEPT	Summary: Experimental evidence confirms FT nuclear localization at the shoot apical meristem where it interacts with FD transcription factors. This is essential for function. Supporting Evidence: PMID:16099979 FD, a bZIP protein mediating signals from the floral pathway integrator FT at the shoot apex.
GO:0005737 cytoplasm	IDA PMID:16099979 FD, a bZIP protein mediating signals from the floral pathway...	ACCEPT	Summary: Experimental evidence confirms FT cytoplasmic localization. FT is synthesized in leaf cytoplasm before transport to the shoot apical meristem. Supporting Evidence: PMID:16099979 FD, a bZIP protein mediating signals from the floral pathway integrator FT at the shoot apex.
GO:0048573 photoperiodism, flowering	IEP PMID:17446353 FT protein movement contributes to long-distance signaling i...	ACCEPT	Summary: FT is a key component of the photoperiodic flowering pathway. It integrates long-day photoperiod signals and promotes flowering. This is a core function of FT. Supporting Evidence: PMID:17446353 Apr 19. FT protein movement contributes to long-distance signaling in floral induction of Arabidopsis. file:ARATH/FT/FT-deep-research-falcon.md CO directly activates FT transcription in leaves; FT is the key floral pathway integrator under long days file:ARATH/FT/FT-deep-research-falcon.md FT expression is activated in leaf phloem companion cells (CCs) under inductive conditions (notably long days), and the FT protein is loaded into sieve elements (SEs) for phloem transport.
GO:0008429 phosphatidylethanolamine binding	ISS PMID:10583961 Activation tagging of the floral inducer FT.	ACCEPT	Summary: FT belongs to the PEBP (phosphatidylethanolamine-binding protein) family. This molecular function is characteristic of the protein family and represents its biochemical activity. Supporting Evidence: PMID:10583961 Activation tagging of the floral inducer FT. file:ARATH/FT/FT-deep-research-falcon.md Reviews emphasize that PEBP-family proteins such as FT do not bind DNA directly, but act through interaction with transcriptional regulators such as bZIP factors in the FD class.
GO:0009911 positive regulation of flower development	IMP PMID:10583960 A pair of related genes with antagonistic roles in mediating...	ACCEPT	Summary: This is the core function of FT. It acts as the mobile floral stimulus (florigen) that promotes flowering by activating floral meristem identity genes. Strong experimental support. Supporting Evidence: PMID:10583960 A pair of related genes with antagonistic roles in mediating flowering signals. file:ARATH/FT/FT-deep-research-falcon.md In Arabidopsis, FT encodes a mobile protein signal produced in leaves that is transported to the SAM, where it triggers the vegetative-to-reproductive phase transition.
GO:0009911 positive regulation of flower development	IMP PMID:10583961 Activation tagging of the floral inducer FT.	ACCEPT	Summary: Core function of FT as florigen. Promotes transition from vegetative to reproductive development by activating floral meristem identity genes. Experimental evidence confirms this essential role. Supporting Evidence: PMID:10583961 Activation tagging of the floral inducer FT. file:ARATH/FT/FT-deep-research-falcon.md FT is not an enzyme and does not catalyze a chemical reaction. Instead, it functions as a mobile signaling protein/transcriptional co-regulator that promotes flowering by forming protein complexes at the SAM with DNA-binding transcription factors.
GO:0140297 DNA-binding transcription factor binding	IPI PMID:16099979 FD, a bZIP protein mediating signals from the floral pathway...	NEW	Summary: NEW annotation. FT directly interacts with the bZIP DNA-binding transcription factors FD/BZIP14 and FDP/BZIP27 at the shoot apical meristem (PMID:16099979, PMID:16099980). This informative molecular function replaces the generic GO:0005515 'protein binding' annotations and captures the specific partner class through which FT, which does not bind DNA itself, acts. Supporting Evidence: PMID:16099979 FD, a bZIP protein mediating signals from the floral pathway integrator FT at the shoot apex. file:ARATH/FT/FT-deep-research-falcon.md Reviews emphasize that PEBP-family proteins such as FT do not bind DNA directly, but act through interaction with transcriptional regulators such as bZIP factors in the FD class.
GO:0003713 transcription coactivator activity	IPI PMID:16099980 Integration of spatial and temporal information during flora...	NEW	Summary: NEW annotation. As the mobile florigen, FT acts as a transcriptional co-regulator: it does not bind DNA directly but, within the florigen activation complex (FT + FD-class bZIPs + 14-3-3), promotes transcriptional activation of floral meristem identity genes such as AP1 at the shoot apical meristem (PMID:16099979, PMID:16099980). This informative molecular function captures FT's positive role in target-gene activation that the generic 'protein binding' terms missed. Evidence code is IPI: GO:0003713 is a molecular function (so IMP is inappropriate), and the coactivator activity is established through FT's physical interaction with the DNA-binding bZIP factor FD that is required to activate AP1 (consistent with the GO definition: activation "via binding to a DNA-binding transcription factor"). Supporting Evidence: PMID:16099980 A complex of FT and FD proteins in turn can activate floral identity genes such as APETALA1 (AP1). file:ARATH/FT/FT-deep-research-falcon.md FT is not an enzyme and does not catalyze a chemical reaction. Instead, it functions as a mobile signaling protein/transcriptional co-regulator that promotes flowering by forming protein complexes at the SAM with DNA-binding transcription factors.

FT

Gene Description

Proposed New Ontology Terms

florigen activation complex assembly

phloem-mediated long-distance protein transport

Existing Annotations Review

Core Functions

Binds the FD/FDP bZIP DNA-binding transcription factors (and redundant partners such as AREB3) at the shoot apical meristem, recruiting them into the florigen activation complex that reprograms gene expression toward floral fate.

References

Suggested Questions for Experts

Suggested Experiments

Deep Research

Falcon

Research report: Functional annotation of FLOWERING LOCUS T (FT) in Arabidopsis thaliana (UniProt Q9SXZ2, locus At1g65480)

1) Verification of correct gene/protein identity (mandatory disambiguation)

2) Key concepts and current understanding (definitions, mechanism, localization)

2.1 Florigen and FT as a systemic flowering signal

2.2 Primary molecular function of FT (what the protein does)

2.3 Tissue, cellular, and subcellular route: where FT is made and where it acts

2.4 Protein complexes and key interactors: how FT induces flowering at the SAM

3) Recent developments and latest research (prioritized 2023–2024)

3.1 Refinements in FT transport control: regulated trafficking machinery

3.2 Quantitative transport timing and localization at the SAM

3.3 Expansion of FT-responsive bZIP network at the SAM (primary research)

3.4 Updated understanding of environmental integration upstream of FT

4) Current applications and real-world implementations (2023–2024)

4.1 Flowering-time and architecture engineering via FT/TFL1 editing (quantitative 2024 example)

4.2 Broader flowering-time engineering strategies and expert synthesis (2023)

5) Expert opinions/analysis and open questions

Evidence-backed summary table

Key sources (with URLs and publication dates)

Notes on limitations of this report

Artifacts

Citations

Perplexity

Citations

📚 Additional Documentation

Falcon Research

Falcon Research Report: FT (ARATH)

📄 View Raw YAML