FD (bZIP14; At4g35900) is a group A basic leucine-zipper (bZIP) transcription factor expressed in the shoot apex before and during the floral transition. FD binds G-box (CACGTG) and related ACGT-containing elements in the nucleus and is the DNA-binding partner of the mobile florigen FLOWERING LOCUS T (FT): FT protein produced in leaf phloem companion cells moves to the shoot apical meristem, where it associates with FD through 14-3-3 proteins that recognize FD phosphorylated at its C-terminal SAP motif (Thr282, a target of the calcium-dependent kinases CPK6 and CPK33). The resulting florigen activation complex activates floral integrator and floral meristem identity genes such as SOC1, LEAFY, APETALA1 and SEPALLATA genes, promoting the transition to flowering; in floral meristems FD with its paralog FDP also supports floral homeotic gene expression. FD is also recruited by the antagonistic PEBP protein TERMINAL FLOWER 1, which competes with FT for chromatin-bound FD to repress the same targets, and FD/FDP contribute to abscisic acid responses in seedlings.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003700 DNA-binding transcription factor activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro bZIP domain mapping to DNA-binding transcription factor activity. Reason: FD is a bZIP transcription factor that binds G-box elements in vivo, but the generic parent term under-describes it: FD binds flowering-gene promoters and, with FT, activates their transcription, so the activator child term is the informative replacement. Proposed replacements: DNA-binding transcription activator activity, RNA polymerase II-specific Supporting Evidence: PMID:32492426 Identical G-box sequences are enriched at FD and FDP binding sites, but only FD binds to genes involved in flowering and only fd alters their transcription. PMID:30770462 Importantly, we observed direct binding of FD to targets involved in several aspects of plant development. PMID:16099980 A complex of FT and FD proteins in turn can activate floral identity genes such as APETALA1 (AP1). |
| GO:0003700 DNA-binding transcription factor activity | ISS PMID:11118137 Arabidopsis transcription factors: genome-wide comparative a... | MODIFY | Summary: Genome-wide transcription factor survey classifying FD (bZIP14) as a transcription factor. Reason: Correct but over-general; ChIP-seq and genetic data show FD acts as a transcriptional activator of floral genes, so the activator child term is preferred. Proposed replacements: DNA-binding transcription activator activity, RNA polymerase II-specific Supporting Evidence: PMID:30770462 Importantly, we observed direct binding of FD to targets involved in several aspects of plant development. |
| GO:0003700 DNA-binding transcription factor activity | ISS PMID:11906833 bZIP transcription factors in Arabidopsis. | MODIFY | Summary: bZIP family review classifying AtbZIP14 (FD) within the bZIP family. Reason: Correct family-level transfer, supported by later direct DNA-binding data; the activator child term captures FD's established role in the florigen activation complex. Proposed replacements: DNA-binding transcription activator activity, RNA polymerase II-specific Supporting Evidence: PMID:11906833 In plants, basic region/leucine zipper motif (bZIP) transcription factors regulate processes including pathogen defence, light and stress signalling, seed maturation and flower development. PMID:32492426 Identical G-box sequences are enriched at FD and FDP binding sites, but only FD binds to genes involved in flowering and only fd alters their transcription. |
| GO:0005515 protein binding | IPI PMID:16099979 FD, a bZIP protein mediating signals from the floral pathway... | MODIFY | Summary: FD interacts with FT (At1g65480) in yeast two-hybrid and in planta assays in Abe et al. 2005; FT is a non-DNA-binding transcriptional co-activator (florigen) recruited to target promoters by FD. Reason: Bare protein binding is uninformative. From FD's side the interaction recruits a transcription coactivator (FT, via 14-3-3), so transcription coactivator binding describes the function. Proposed replacements: transcription coactivator binding Supporting Evidence: PMID:16099979 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). |
| GO:0005515 protein binding | IPI PMID:16099979 FD, a bZIP protein mediating signals from the floral pathway... | REMOVE | Summary: Reported FD interaction with its paralog FDP (bZIP27; UniProtKB:Q7PCC6), attributed to Abe et al. 2005; the cached abstract does not mention FDP, so the assay is in full text not available in the cache. Reason: Generic protein binding is uninformative. Removal does not challenge the reported interaction, but no in vivo FD-FDP dimerization role is established: later genetic analysis argues that FD is unlikely to be the heterodimerization partner of FDP, so a more specific replacement such as protein heterodimerization activity is not warranted. Supporting Evidence: PMID:32492426 The proposed heterodimerization partner of FDP is unlikely to be FD because fdp-1 and fdp-2 enhanced the late-flowering phenotype of fd-3 mutants |
| GO:0005515 protein binding | IPI PMID:16099979 FD, a bZIP protein mediating signals from the floral pathway... | MODIFY | Summary: FD-FT interaction (UniProtKB:Q9SXZ2) from Abe et al. 2005. Reason: Same interaction as the AGI-keyed row; transcription coactivator binding is more informative. Proposed replacements: transcription coactivator binding Supporting Evidence: PMID:16099979 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). |
| GO:0005515 protein binding | IPI PMID:16099980 Integration of spatial and temporal information during flora... | MODIFY | Summary: Wigge et al. 2005 show FT and FD proteins form a complex that activates AP1. Reason: Transcription coactivator binding captures recruitment of FT (a non-DNA-binding co-activator) by FD. Proposed replacements: transcription coactivator binding Supporting Evidence: PMID:16099980 A complex of FT and FD proteins in turn can activate floral identity genes such as APETALA1 (AP1). |
| GO:0005515 protein binding | IPI PMID:19656342 Genetic and spatial interactions between FT, TSF and SVP dur... | MODIFY | Summary: Jang et al. 2009 show FT and TSF interact in yeast with the same bZIP factors including FD. Reason: Same FD-FT interaction; transcription coactivator binding is more informative. Proposed replacements: transcription coactivator binding Supporting Evidence: PMID:19656342 we demonstrate that TSF and FT have similar biochemical functions by showing that they interact in yeast with the same bZIP transcription factors. |
| GO:0005634 nucleus | EXP PMID:25661797 Calcium-dependent protein kinases responsible for the phosph... | ACCEPT | Summary: EGFP-FD expressed from the FD promoter localizes to the nucleus of shoot apical cells regardless of phosphorylation state. Reason: Direct localization evidence. Supporting Evidence: PMID:25661797 These results indicate that FD is constitutively localized in the nucleus in a phosphorylation-independent manner. |
| GO:0005634 nucleus | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA for nucleus across group A bZIPs (ABF/ABI5/FD clade); FD (At4g35900) is among the descendants with experimental support. Reason: Nuclear activity is expected for a bZIP transcription factor and is experimentally confirmed for FD. Supporting Evidence: PMID:25661797 These results indicate that FD is constitutively localized in the nucleus in a phosphorylation-independent manner. |
| GO:0005634 nucleus | IDA PMID:16099979 FD, a bZIP protein mediating signals from the floral pathway... | ACCEPT | Summary: Abe et al. 2005 localized FD to the nucleus (abstract cached; the nuclear localization is reported in the full text). Reason: Consistent with independent EGFP-FD localization data. Supporting Evidence: PMID:25661797 These results indicate that FD is constitutively localized in the nucleus in a phosphorylation-independent manner. |
| GO:0005634 nucleus | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular location mapping to nucleus. Reason: Consistent with experimental data. Supporting Evidence: PMID:25661797 These results indicate that FD is constitutively localized in the nucleus in a phosphorylation-independent manner. |
| GO:0005634 nucleus | ISM GO_REF:0000122 | ACCEPT | Summary: AtSubP prediction of nuclear localization. Reason: Consistent with experimental data. Supporting Evidence: PMID:25661797 These results indicate that FD is constitutively localized in the nucleus in a phosphorylation-independent manner. |
| GO:0006355 regulation of DNA-templated transcription | IDA PMID:16099979 FD, a bZIP protein mediating signals from the floral pathway... | ACCEPT | Summary: FD and FT act together to activate AP1 transcription at the shoot apex. Reason: Correct, if general; FD regulates transcription of floral identity genes. Supporting Evidence: PMID:16099979 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). |
| GO:0006355 regulation of DNA-templated transcription | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro bZIP mapping to regulation of DNA-templated transcription. Reason: Correct, general. Supporting Evidence: PMID:32492426 Identical G-box sequences are enriched at FD and FDP binding sites, but only FD binds to genes involved in flowering and only fd alters their transcription. |
| GO:0009648 photoperiodism | IMP PMID:9615462 EMF genes interact with late-flowering genes to regulate Ara... | KEEP AS NON CORE | Summary: Haung and Yang 1998 analysed emf double mutants with late-flowering mutants including fd; Koornneef et al. 1991 showed fd mutants are late flowering and respond to photoperiod. Reason: FD acts downstream of photoperiod perception (as the shoot-apex partner of FT), so photoperiodism is an upstream context rather than a process FD performs; acceptable as acts_upstream_of_or_within but not core. Supporting Evidence: PMID:9615462 Nine late-flowering mutants, ft, fca, ld, fd, fpa, fe, fy, fha, and fve, caused different degrees of increase in the number of sessile leaves |
| GO:0009909 regulation of flower development | IGI PMID:16099979 FD, a bZIP protein mediating signals from the floral pathway... | ACCEPT | Summary: Genetic interaction of fd with ft/AP1 pathway genes in Abe et al. 2005. Reason: FD is required for FT to promote flowering and activate AP1; regulation of flower development is appropriate. Supporting Evidence: PMID:16099979 A bZIP transcription factor, FD, preferentially expressed in the shoot apex is required for FT to promote flowering. PMID:16099979 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). |
| GO:0009911 positive regulation of flower development | IMP PMID:1896021 A genetic and physiological analysis of late flowering mutan... | ACCEPT | Summary: fd mutants are late flowering (Koornneef et al. 1991). Reason: Loss of FD delays flowering; FD promotes the floral transition. Consistent with the core process. Supporting Evidence: PMID:1896021 whereas co, gi, fd and fwa mutants are almost completely insensitive to this treatment. |
| GO:0045893 positive regulation of DNA-templated transcription | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro mapping to positive regulation of transcription. Reason: FD-FT activate target genes such as AP1 and SEP genes. Supporting Evidence: PMID:16099980 A complex of FT and FD proteins in turn can activate floral identity genes such as APETALA1 (AP1). |
| GO:0045893 positive regulation of DNA-templated transcription | IMP PMID:16099980 Integration of spatial and temporal information during flora... | ACCEPT | Summary: Wigge et al. 2005: the FT-FD complex activates floral identity genes such as AP1. Reason: Correct; FD is an activator in the florigen complex. Supporting Evidence: PMID:16099980 A complex of FT and FD proteins in turn can activate floral identity genes such as APETALA1 (AP1). |
| GO:2000028 regulation of photoperiodism, flowering | IMP PMID:16099979 FD, a bZIP protein mediating signals from the floral pathway... | ACCEPT | Summary: FD is required for FT, the output of the photoperiod pathway, to promote flowering. Reason: FD is the shoot-apex effector of photoperiodic FT signalling; regulation of photoperiodism, flowering is appropriate. Supporting Evidence: PMID:16099979 A bZIP transcription factor, FD, preferentially expressed in the shoot apex is required for FT to promote flowering. |
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Download this section (compressed HTML)Q: Is FT binding required for FD to bind its flowering targets in vivo, or does FT mainly convert pre-bound FD (also used by TFL1) from a repressive to an activating complex?
Q: What is the in vivo dimerization partner of FD at the shoot apex, given that FDP is expressed in largely complementary domains?
Experiment: Compare FD ChIP-seq in wild type, ft tsf and tfl1 apices with phospho-null (T282A) and phosphomimic FD alleles to separate the contributions of FT/TFL1 and 14-3-3 binding to FD occupancy and target activation.
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