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.
Definition: The formation of a transcriptional activation complex containing florigen (FT) and bZIP transcription factors that activates floral meristem identity gene expression
Justification: FT forms the florigen activation complex (FAC) with FD/FDP transcription factors, which is essential for activating floral development genes
Parent term: regulation of flower development
Supporting Evidence:
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
Justification: FT represents a paradigm for long-distance protein signaling through the phloem vascular system from leaves to the shoot apical meristem
Parent term: protein transport
Supporting Evidence:
| 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. |
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Download this section (compressed HTML)Q: 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?
Q: 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?
Q: 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?
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
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