OsFTL1 integrates circadian and photoperiodic signals to optimize flowering time for ecological adaptation in rice

The development of early-maturing rice (Oryza sativa L.) varieties is critical for enhancing regional adaptability, requiring precise flowering time regulation without compromising yield. We show that natural variation in OsFTL1, encoding a phosphatidylethanolamine-binding protein, integrates circadian and photoperiod pathways to control heading date. The agronomically valuable OsFTL1 allele from the NIL(qHD1b) line consistently accelerates flowering by approximately one week compared to the OsFTL1 allele from ZH8015 in multi-environment trials while preserving yield, with transgenic analyses confirming its dosage-dependent flowering promotion. At the molecular level, we demonstrate that OsFTL1 functions as a florigen downstream of the central integrator Ehd1, defining a florigenic branch parallel to Hd3a and RFT1. OsFTL1 physically interacts with the flowering repressor Ghd7, which competitively inhibits its association with the 14-3-3 protein GF14c, thereby post-translationally regulating florigen activation complex formation. The circadian oscillator OsCCA1 directly activates OsFTL1 through polymorphic MYB binding sites, with the NIL(qHD1b) promoter showing enhanced responsiveness due to an additional site. Population genetic analyses revealed strong selection on OsFTL1 regulatory variation during japonica's northern expansion, with distinct haplotypes exhibiting different promoter activities and cis-element compositions. Collectively, our study elucidates how OsFTL1 coordinates the trade-off between early maturity and yield through integrated environmental and endogenous signals, establishing a novel regulatory paradigm for ecological adaptation in rice and providing allele-specific strategies for molecular design breeding.