Photoperiodic (long-day) flowering via the CONSTANS-FLOWERING LOCUS T pathway (Arabidopsis)

The external-coincidence mechanism by which Arabidopsis measures day length and converts long days into flowering. In leaf phloem companion cells the morning-phased Dof repressors (CYCLING DOF FACTORs, represented by CDF1) bind the CONSTANS (CO) and FLOWERING LOCUS T (FT) promoters and repress them, partly by recruiting TOPLESS. In long-day afternoons the clock-phased FKF1 and GIGANTEA (GI) proteins coincide with light; blue-light activation of the FKF1 LOV domain promotes FKF1-GI complex formation on the CO promoter and SCF(FKF1)-dependent degradation of the CDFs, relieving CO repression. CO protein is unstable in the dark because the COP1-SPA E3 ubiquitin ligase targets it for proteasomal degradation; in the light, photoactivated CRY2 (blue) and phyA (far-red) inhibit COP1-SPA and FKF1 binds and stabilizes CO, so CO protein accumulates only when CO mRNA expression overlaps with light at the end of a long day. CO, in an NF-Y-like trimer with NF-YB/NF-YC, binds CORE (CCACA) elements and activates FT transcription in companion cells. FT protein (florigen) moves through the phloem to the shoot apical meristem, where 14-3-3 proteins bridge it to the phosphorylated bZIP transcription factor FD; this florigen activation complex activates floral integrator and floral meristem identity genes such as SOC1 and AP1, committing the meristem to flowering. The circadian oscillator that phases GI, FKF1, CDF and CO expression, phytochrome-mediated photomorphogenesis, FT transport machinery and the vernalization/autonomous pathways are outside this module.

MODULE:photoperiodic_flowering_co_ftDRAFTCONCRETESignaling Pathwaymodules/photoperiodic_flowering_co_ft.yaml
long-day photoperiodism, floweringGO:0048574
PMID:17872410
FKF1 and GIGANTEA complex formation is required for day-length measurement in Arabidopsis.
Blue-light-dependent FKF1-GI complex on the CO promoter controls CDF1 stability and CO timing.
Thus, the FKF1-GI complex forms on the CO promoter in late afternoon to regulate CO expression, providing a mechanistic view of how the coincidence of light with circadian timing regulates photoperiodic flowering.
PMID:22628657
FKF1 conveys timing information for CONSTANS stabilization in photoperiodic flowering.
FKF1 both stabilizes CO protein and removes CDF1 repressors from CO and FT.
In addition, FKF1 simultaneously removes CYCLING DOF FACTOR 1 (CDF1), which represses CO and FLOWERING LOCUS T (FT) transcription.
PMID:18296627
COP1-mediated ubiquitination of CONSTANS is implicated in cryptochrome regulation of flowering in Arabidopsis.
CO is degraded in darkness by COP1, stabilized by cryptochrome signalling, and activates FT in leaves; FT protein moves to the shoot apex.
Under LDs, the transcription of FLOWERING LOCUS T (FT) is activated by CONSTANS (CO) in leaf, and the FT protein moves to the shoot apex to induce flowering.
PMID:17446353
FT protein movement contributes to long-distance signaling in floral induction of Arabidopsis.
FT protein produced in phloem moves to the apex as a long-distance signal.
We conclude that FT protein acts as a long-distance signal that induces Arabidopsis flowering.
PMID:16099979
FD, a bZIP protein mediating signals from the floral pathway integrator FT at the shoot apex.
FD and FT act together at the shoot apex to activate AP1.
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).

Concrete Arabidopsis instance; each annoton is grounded on a reviewed gene in genes/ARATH and its function term matches that review's core_functions. CDF1 represents the redundant CDF1/2/3/5 repressors; LKP2 and the COP1 partners SPA2-4 are omitted for compactness. ZTL is included as an optional, minor contributor to CDF turnover; it is better known for its clock role (separate module). The ZTL annoton is grounded on the Swiss-Prot entry Q94BT6 (ADO1_ARATH, At5g57360), to which the ZTL gene review was re-grounded from the alternative gene-model entry F4KAN2. Circadian oscillator components (CCA1/LHY, PRRs, TOC1, ELF3/ELF4/LUX) that phase GI, FKF1, CDF and CO expression, and phytochrome-B photomorphogenesis, are context modules and are referenced only in prose. 14-3-3 proteins of the florigen activation complex, NF-YB/NF-YC partners of CO, and FT transport factors (FTIP1, NaKR3) are not modelled. The SPA1 annoton (UniProtKB:Q9SYX2) is grounded on the ARATH/SPA1 review, which this branch carries. No production GO-CAM in gocams/index.tsv contains these Arabidopsis gene products, so no gocam_associations are given.

6Nodes
5Parts
0Variant Sets
0Variants
13Annotons
4Connections

Derived QC

Recommended-field compliance

100.0% recommended fields populated

All recommended fields populated.

Module deep research

✗ none found

No MODULE:photoperiodic_flowering_co_ft deep-research report alongside the module YAML.

Leaf nodes lacking representative members

✓ every leaf node grounds to a representative protein.

Template conformance

✓ every declared conforms_to bundle matches its template motif.

Function consistency and core coverage

13 gene-function check(s) reflected in core functions · 0 conflict(s) · 0 evidence or coverage gap(s) (13 comparison(s))

Retained noncore functions are reported separately; they do not require promotion to core functions. Support from representative genes does not establish conservation across the whole family. Missing reviews or identifiers leave a claim unverified.

AnnotonParticipantFunctionAssessment
fkf1_blue_light_photoreceptor FKF1 (At1g68050)
UniProtKB:Q9C9W9
Gene 		photoreceptor activity
GO:0009881 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
fkf1_scf_substrate_adaptor FKF1 (At1g68050)
UniProtKB:Q9C9W9
Gene 		ubiquitin-like ligase-substrate adaptor activity
GO:1990756 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gi_fkf1_partner GIGANTEA (At1g22770)
UniProtKB:Q9SQI2
Gene 		ubiquitin protein ligase binding
GO:0031625 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
ztl_minor_cdf_adaptor ZEITLUPE (At5g57360)
UniProtKB:Q94BT6
Gene 		ubiquitin-like ligase-substrate adaptor activity
GO:1990756 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
cdf1_repressor CDF1 (At5g62430)
UniProtKB:Q8W1E3
Gene 		DNA-binding transcription repressor activity, RNA polymerase II-specific
GO:0001227 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
cop1_e3_ligase COP1 (At2g32950)
UniProtKB:P43254
Gene 		ubiquitin protein ligase activity
GO:0061630 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
spa1_cop1_activator SPA1 (At2g46340)
UniProtKB:Q9SYX2
Gene 		ubiquitin-protein transferase activator activity
GO:0097027 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
cry2_blue_light_receptor CRY2 (At1g04400)
UniProtKB:Q96524
Gene 		blue light photoreceptor activity
GO:0009882 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
phya_far_red_receptor PHYA (At1g09570)
UniProtKB:P14712
Gene 		far-red light photoreceptor activity
GO:0031516 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
co_ft_activator CONSTANS (At5g15840)
UniProtKB:Q39057
Gene 		DNA-binding transcription activator activity, RNA polymerase II-specific
GO:0001228 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
ft_florigen_coactivator FLOWERING LOCUS T (At1g65480)
UniProtKB:Q9SXZ2
Gene 		transcription coactivator activity
GO:0003713 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
fd_bzip_activator FD (At4g35900)
UniProtKB:Q84JK2
Gene 		DNA-binding transcription activator activity, RNA polymerase II-specific
GO:0001228 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
soc1_floral_integrator SOC1 (At2g45660)
UniProtKB:O64645
Gene 		DNA-binding transcription factor activity, RNA polymerase II-specific
GO:0000981 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).

Feedback loops (advisory, prose-driven: a regulator counts as "feedback" when its own description says so)

✓ every negative regulator described as feedback has an upstream edge closing the loop.

  • cdf_clearance ⊣ cdf_repression [input]
    cdf_clearance is a negative regulator with no upstream edge (not described as feedback)
  • cdf_repression ⊣ ft_induction [input]
    cdf_repression is a negative regulator with no upstream edge (not described as feedback)
  • co_stabilization ⊣ ft_induction [input]
    co_stabilization is a negative regulator with no upstream edge (not described as feedback)

Gene-review completeness (12/12 grounded genes reviewed)

12 complete review(s) · 10 with deep research · 0 missing review · 2 reviewed but lacking deep research

Gene Review Complete Deep research
CDF1 Q8W1E3 ✓ ✓ ✗
CO Q39057 ✓ ✓ ✓
COP1 P43254 ✓ ✓ ✓
CRY2 Q96524 ✓ ✓ ✓
FD Q84JK2 ✓ ✓ ✗
FKF1 Q9C9W9 ✓ ✓ ✓
FT Q9SXZ2 ✓ ✓ ✓
GI Q9SQI2 ✓ ✓ ✓
PHYA P14712 ✓ ✓ ✓
SOC1 O64645 ✓ ✓ ✓
SPA1 Q9SYX2 ✓ ✓ ✓
ZTL Q94BT6 ✓ ✓ ✓

Details

Context
Arabidopsis thalianaNCBITaxon:3702
nucleusGO:0005634
Photoperiodic flowering via CO-FTSignaling Pathwayphotoperiodic_flowering_co_ft
long-day photoperiodism, floweringGO:0048574
Context
Arabidopsis thalianaNCBITaxon:3702
nucleusGO:0005634

Connections

cdf_clearance -> cdf_repression Negatively Regulates
FKF1-GI-dependent degradation removes CDF repressors from CO and FT promoters in long-day afternoons.
PMID:22628657
FKF1 removes CDF1, which represses CO and FT.
FKF1 simultaneously removes CYCLING DOF FACTOR 1 (CDF1), which represses CO and FLOWERING LOCUS T (FT) transcription.
cdf_repression -> ft_induction Negatively Regulates
CDFs repress CO transcription and FT transcription directly.
co_stabilization -> ft_induction Negatively Regulates
COP1-SPA-mediated degradation of CO limits FT activation; photoreceptor inhibition of COP1-SPA (and FKF1 binding to CO) relieves this in the light.
ft_induction -> florigen_action Provides Input For
FT protein made in companion cells travels through the phloem to the shoot apex.
Part 1: blue-light-gated clearance of CDF repressors
FKF1-GI-dependent degradation of CDF repressorsRegulatory Stepcdf_clearance

In long-day afternoons, blue light absorbed by the FKF1 LOV domain promotes FKF1-GI complex formation; SCF(FKF1) binds the CDF repressors on the CO and FT promoters and targets them for proteasomal degradation.

Annotons

FKF1: LOV-domain blue-light photoreceptor
fkf1_blue_light_photoreceptor
Participant: Gene Product: FKF1 (At1g68050)
Gene Product:
FKF1 (At1g68050)UniProtKB:Q9C9W9

Function

photoreceptor activityGO:0009881

Processes

response to blue lightGO:0009637

Locations

nucleusGO:0005634

Senses blue light in the afternoon through its flavin-binding LOV domain; light enhances binding to GI.

PMID:17872410
FKF1 and GI form a complex in a blue-light-dependent manner.
We demonstrate that FKF1 and GI proteins form a complex in a blue-light-dependent manner.
FKF1: SCF substrate adaptor for CDF degradation
fkf1_scf_substrate_adaptor
Participant: Gene Product: FKF1 (At1g68050)
Gene Product:
FKF1 (At1g68050)UniProtKB:Q9C9W9

Function

ubiquitin-like ligase-substrate adaptor activityGO:1990756

Processes

ubiquitin-dependent protein catabolic processGO:0006511

Locations

nucleusGO:0005634

F-box subunit that recruits CDF1 and its homologs to SCF for degradation.

PMID:16002617
FKF1 binds CDF1 and is required for its daily degradation.
FKF1 physically interacts with CDF1, and CDF1 protein is more stable in fkf1 mutants.
GI: FKF1-binding partner required for CDF turnover
gi_fkf1_partner
Participant: Gene Product: GIGANTEA (At1g22770)
Gene Product:
GIGANTEA (At1g22770)UniProtKB:Q9SQI2

Function

ubiquitin protein ligase bindingGO:0031625

Processes

positive regulation of long-day photoperiodism, floweringGO:0048578

Locations

nucleusGO:0005634

Binds and stabilizes FKF1 (and ZTL), binds CDF1, and is needed for FKF1-dependent CDF degradation on the CO promoter.

PMID:17872410
FKF1 function depends on GI, which binds CDF1 and controls its stability.
FKF1 function is dependent on GI, which interacts with a CO repressor, CYCLING DOF FACTOR 1 (CDF1), and controls CDF1 stability.
PMID:19619493
GI stabilizes FKF1, reducing CDF2 abundance.
We show that GI stabilizes FKF1, thereby reducing CDF2 abundance and allowing transcription of CO.
ZTL: FKF1-family F-box adaptor (minor CDF contribution)
ztl_minor_cdf_adaptor
Participant: Gene Product: ZEITLUPE (At5g57360)
Gene Product:
ZEITLUPE (At5g57360)UniProtKB:Q94BT6

Function

ubiquitin-like ligase-substrate adaptor activityGO:1990756

Processes

SCF-dependent proteasomal ubiquitin-dependent protein catabolic processGO:0031146

FKF1/LKP2 paralog that, like FKF1, is stabilized by GI and contributes redundantly to CDF degradation; its main role is in clock protein turnover, and it is modelled here only as a minor contributor to CDF clearance.

PMID:25600594
GI stabilizes the F-box proteins FKF1, ZTL and LKP2 to degrade CDF proteins.
A major function of GI is to stabilize the F–box proteins FKF1, ZTL and LKP2 to degrade CDF proteins, promoting CO and FT transcription and flowering

Optional; see ZTL review and the circadian clock module for its primary role.

Part 2: morning repression of CO and FT transcription
CDF repression of CO and FTRegulatory Stepcdf_repression

Morning-phased CDF Dof factors bind Dof sites in the CO and FT promoters in companion cells and repress transcription, in part through the TOPLESS co-repressor.

Annotons

CDF1: Dof transcriptional repressor of CO and FT
cdf1_repressor
Participant: Gene Product: CDF1 (At5g62430)
Gene Product:
CDF1 (At5g62430)UniProtKB:Q8W1E3

Function

DNA-binding transcription repressor activity, RNA polymerase II-specificGO:0001227

Processes

negative regulation of long-day photoperiodism, floweringGO:0048579

Locations

nucleusGO:0005634

Represses CO and FT; represents the redundant CDF1/2/3/5 group.

PMID:16002617
CDF1 binds the CO promoter and represses CO.
CDF1 and CO are expressed in the same tissues, and CDF1 binds to the CO promoter.
PMID:22628657
CDF1 represses FT directly.
These results indicate that CDF1 protein represses FT transcription independently of CO transcription.
PMID:28752516
TPL recruitment confers CDF1 repressive activity.
This TPL interaction confers a repressive function on CDF1, as mutations of the N-terminal TPL binding domain largely impair the ability of CDF1 protein to repress its targets.
Part 3: COP1-SPA degradation of CO and its light-dependent inhibition
COP1-SPA degradation of CO and its photoreceptor inhibitionRegulatory Stepco_stabilization

In darkness the COP1-SPA E3 ligase ubiquitinates CO for proteasomal degradation. Blue-light activated CRY2 binds SPA1 and COP1 and suppresses COP1-SPA activity; phyA and cryptochrome light signals stabilize CO protein in long days; FKF1 binds and stabilizes CO in long-day afternoons.

Annotons

COP1: E3 ubiquitin ligase degrading CO at night
cop1_e3_ligase
Participant: Gene Product: COP1 (At2g32950)
Gene Product:
COP1 (At2g32950)UniProtKB:P43254

Function

ubiquitin protein ligase activityGO:0061630

Processes

proteasome-mediated ubiquitin-dependent protein catabolic processGO:0043161

Locations

nucleusGO:0005634
PMID:18296627
COP1 ubiquitinates CO and reduces CO levels.
In addition, COP1 physically interacts with CO and functions as an E3 ligase, ubiquitinating CO in vitro and reducing CO levels in vivo.
SPA1: COP1-associated activator of CO degradation
spa1_cop1_activator
Participant: Gene Product: SPA1 (At2g46340)
Gene Product:
SPA1 (At2g46340)UniProtKB:Q9SYX2

Function

ubiquitin-protein transferase activator activityGO:0097027

Locations

nucleusGO:0005634

Represents SPA1-4; enhances COP1 E3 activity toward CO.

PMID:21514160
SPA1 mediates blue-light suppression of COP1-dependent CO proteolysis downstream of CRY2.
We demonstrate that SPA1 acts genetically downstream from CRY2 to mediate blue light suppression of the COP1-dependent proteolysis of the flowering-time regulator CONSTANS (CO).
CRY2: blue-light receptor inhibiting COP1-SPA
cry2_blue_light_receptor
Participant: Gene Product: CRY2 (At1g04400)
Gene Product:
CRY2 (At1g04400)UniProtKB:Q96524

Function

blue light photoreceptor activityGO:0009882

Processes

blue light signaling pathwayGO:0009785

Locations

nucleusGO:0005634
PMID:21514160
Blue-light-dependent CRY2-SPA1 interaction stimulates CRY2-COP1 interaction.
We further show that blue light-dependent CRY2-SPA1 interaction stimulates CRY2-COP1 interaction.
phyA: far-red light receptor contributing to CO stabilization
phya_far_red_receptor
Participant: Gene Product: PHYA (At1g09570)
Gene Product:
PHYA (At1g09570)UniProtKB:P14712

Function

far-red light photoreceptor activityGO:0031516

Processes

far-red light signaling pathwayGO:0010018

Far-red/dusk light input that stabilizes CO protein (with CRY2) late in long days; primary phyA photomorphogenesis roles belong to a separate module.

PMID:14963328
Photoreceptors regulate CO protein stability; light stabilizes nuclear CO in the evening.
We show that light stabilizes nuclear CO protein in the evening, whereas in the morning or in darkness the protein is degraded by the proteasome.
PMID:22628657
phyA and cryptochrome light signals stabilize CO protein in long days.
Light signals perceived by phytochrome A (phyA) and cryptochrome (cry) photoreceptors stabilize CO protein in long days
PMID:18388858
phyA and cry2 mutations delay flowering and reduce CO protein accumulation.
Mutations in the genes encoding the photoreceptors phytochrome A (phyA) and cryptochrome 2 (cry2) delay flowering, and these mutations also reduce the accumulation of CO protein

Grounded via the PHYA gene review. The primary study (Valverde et al. 2004, PMID:14963328) is cached as abstract only, which names photoreceptors generically; the phyA-specific statements are from later cached full texts citing it.

Part 4: CO activation of FT in phloem companion cells
CO-dependent FT transcription in leaf companion cellsRegulatory Stepft_induction

Stabilized CO forms an NF-Y-like trimer with NF-YB/NF-YC, binds CORE (CCACA) elements in the FT promoter and activates FT transcription in leaf phloem companion cells.

Annotons

CO: DNA-binding transcriptional activator of FT
co_ft_activator
Participant: Gene Product: CONSTANS (At5g15840)
Gene Product:
CONSTANS (At5g15840)UniProtKB:Q39057

Function

DNA-binding transcription activator activity, RNA polymerase II-specificGO:0001228

Processes

positive regulation of long-day photoperiodism, floweringGO:0048578

Locations

nucleusGO:0005634
PMID:28526714
CO-NF-YB/NF-YC trimer binds the FT CORE element.
forms a trimer with Arabidopsis thaliana NF-YB2/NF-YC3 to efficiently bind the CORE element of the FLOWERING LOCUS T promoter.
Part 5: florigen action at the shoot apical meristem
FT-FD florigen activation complex at the shoot apexRegulatory Stepflorigen_action

FT protein, after phloem transport to the shoot apex, binds 14-3-3 proteins and the phosphorylated bZIP FD; the complex activates SOC1, AP1 and other floral genes, and SOC1 relays the signal to floral meristem identity genes.

Annotons

FT: mobile florigen, transcription coactivator
ft_florigen_coactivator
Participant: Gene Product: FLOWERING LOCUS T (At1g65480)
Gene Product:
FLOWERING LOCUS T (At1g65480)UniProtKB:Q9SXZ2

Function

transcription coactivator activityGO:0003713

Processes

positive regulation of flower developmentGO:0009911

Locations

nucleusGO:0005634
PMID:17446353
FT protein expressed in phloem moves to the apex.
FT fusion proteins expressed specifically in phloem cells move to the apex and move long distances between grafted plants.
FD: bZIP DNA-binding partner of FT
fd_bzip_activator
Participant: Gene Product: FD (At4g35900)
Gene Product:
FD (At4g35900)UniProtKB:Q84JK2

Function

DNA-binding transcription activator activity, RNA polymerase II-specificGO:0001228

Processes

positive regulation of flower developmentGO:0009911

Locations

nucleusGO:0005634
PMID:16099980
A complex of FT and FD activates floral identity genes.
A complex of FT and FD proteins in turn can activate floral identity genes such as APETALA1 (AP1).
PMID:25661797
FD Thr282 phosphorylation by CPKs is needed for 14-3-3-mediated complex formation with FT.
which is a crucial residue for the complex formation with FT via 14-3-3.
SOC1: MADS-box floral integrator downstream of FT-FD
soc1_floral_integrator
Participant: Gene Product: SOC1 (At2g45660)
Gene Product:
SOC1 (At2g45660)UniProtKB:O64645

Function

DNA-binding transcription factor activity, RNA polymerase II-specificGO:0000981

Processes

vegetative to reproductive phase transition of meristemGO:0010228

Locations

nucleusGO:0005634

Output integrator gene activated at the apex by the florigen complex.

PMID:30770462
SOC1 is a high-confidence in vivo FD target at the shoot apex.
The 595 peak regions shared between the replicates mapped to 572 individual genes, which we consider high-confidence in vivo targets of FD at the SAM and include important flowering-related genes such as AP1 , FUL , SOC1 , and SEP3 .
PMID:30770462
FD overexpression strongly induces SOC1.
Reverse transcription quantitative-PCR (RT-qPCR) assays confirmed that both SOC1 and AP1 were strongly upregulated in p35S :: FD