Florigen-like protein OsFTL1 promotes flowering without essential florigens Hd3a and RFT1 in rice.

Abstract

Flowering time is a critical agronomic trait in rice, directly influencing grain yield and adaptability to specific planting regions and seasons. Florigens, including FLOWERING LOCUS T (FT) proteins Hd3a (OsFTL2) and RFT1 (OsFTL3), play central roles in transmitting flowering signals through rice's photoperiod regulatory network. While Hd3a and RFT1 have been extensively studied, the functions and interactions of other FT-like proteins remain unclear, limiting advancements in breeding strategies for early-maturing rice varieties. Here, we demonstrate that the florigen-like protein OsFTL1 forms a florigen activation complex (FAC) and promotes flowering under both short-day and long-day conditions. OsFTL1 localizes to the nucleus and cytoplasm, with predominant expression in the shoot base, facilitating its mobilization to the shoot apical meristem (SAM) to initiate flowering. Overexpression of OsFTL1 (OsFTL1-OE) in leaves or shoot bases significantly accelerates flowering and alters plant architecture. In the nucleus, OsFTL1 interacts with GF14c and OsFD1 to form an FAC, activating OsMADS14 and OsMADS15 expression to drive flowering. Markedly, OsFTL1-OE plants deficient in Hd3a and RFT1 exhibited earlier flowering compared with wild-type plants, indicating that OsFTL1 can independently promote flowering. Furthermore, haplotype analysis identified OsFTL1-Hap3, a beneficial variant associated with early flowering and comparable grain yields. These findings revealed that OsFTL1 can substitute for Hd3a and RFT1 in FAC formation, promoting flowering across photoperiods, and highlighting its potential application in breeding early-maturing, high-yield rice varieties suitable for diverse environments.