| Category | Key points | Evidence citation IDs |
|---|---|---|
| Identity/definition | HD3A in rice corresponds to Os06g0157700 and is the rice FT ortholog/florigen; it encodes a small FT-like phosphatidylethanolamine-binding protein (PEBP) family member that promotes flowering, especially under short days. | (pqac-00000005, pqac-00000012, pqac-00000014) |
| Expression | Hd3a transcription is concentrated in leaf blade vascular tissue/phloem-associated cells and is very low in the shoot apex; expression is induced under short days and falls sharply under long days, with reported strong reduction when day length exceeds ~13.5 h. | (pqac-00000000, pqac-00000012, pqac-00000014) |
| Mobility/transport | Hd3a protein is synthesized in leaves, loaded into phloem, transported long distance toward the shoot apical meristem (SAM), unloaded near the vascular termini, and then enters the SAM; transport is central to florigen function, while some trafficking steps remain unresolved. | (pqac-00000000, pqac-00000002, pqac-00000009, pqac-00000010, pqac-00000014) |
| Subcellular localization | In SAM cells, Hd3a first forms a cytoplasmic Hd3a–14-3-3 subcomplex; nuclear function depends on OsFD1 co-expression, and Hd3a accumulation in the SAM is spatially restricted during floral transition. Classic localization studies also detected Hd3a-GFP in vasculature and the inner SAM region. | (pqac-00000009, pqac-00000014) |
| Molecular interactions | Hd3a interacts with 14-3-3 proteins (GF14 family) and OsFD1 to form the florigen activation complex (FAC); 14-3-3 interaction is essential for activity. Antagonistic PEBP proteins such as RCNs/OsFTL4 can compete for 14-3-3 binding, forming repression complexes or attenuating florigen output. | (pqac-00000003, pqac-00000005, pqac-00000009) |
| Downstream targets | The FAC activates flowering MADS-box genes, especially OsMADS15 and also OsMADS14/15 in rice, linking Hd3a arrival at the SAM to floral transition and meristem identity reprogramming. | (pqac-00000003, pqac-00000005, pqac-00000007) |
| Upstream regulators | Hd3a is positively regulated by Hd1 and Ehd1; modulators include OsGI, OsMADS50, OsMADS51, Ghd7 and circadian/photoperiod inputs. Hd1 can activate or repress depending on daylength context, while Ehd1 is a major promoter of Hd3a expression. | (pqac-00000004, pqac-00000006, pqac-00000016) |
| Quantitative phenotypes | Functional perturbation causes large flowering phenotypes: Hd3a RNAi delayed flowering by >30 days, and double suppression of Hd3a and RFT1 prevented flowering up to 300 days; Hd3a expression is reduced to <1/10 above ~13.5 h day length, and a 10-min night break can block induction and delay flowering. | (pqac-00000002, pqac-00000012) |
| Recent developments 2023-2024 | Recent reviews emphasize a refined model in which Hd3a forms the FAC after cytoplasmic interaction with 14-3-3, then acts in/around the SAM; major open questions include exact unloading routes, intra-SAM distribution, transport cofactors, and how a restricted Hd3a domain triggers whole-SAM transition. | (pqac-00000009, pqac-00000010, pqac-00000013) |
| Applications | Hd3a-centered flowering networks are active targets for crop adaptation and breeding: recent studies manipulate upstream regulators or parallel florigen pathways to tune Hd3a/RFT1 expression and heading date for regional adaptation, quality, and yield; reviews highlight heading-date engineering as a practical route for rice improvement. | (pqac-00000011, pqac-00000015) |


*Table: This table summarizes core functional-annotation evidence for rice HD3A/Os06g0157700, covering identity, mechanism, localization, regulation, phenotypes, and recent translational relevance. It is designed as a compact evidence map for use in a research report.*