Rice OsFKF1 Promotes Degradation of OsPRR37 for Short-Day Early Flowering

Many plant species use changes in day length to fine-tune flowering time and achieve successful reproduction under optimal conditions. Extensive molecular genetic studies have identified key regulatory genes that repress flowering under non-inductive long-day (LD) conditions in rice (Oryza sativa), a facultative short-day (SD) plant. However, understanding how these regulators are modulated at the post-translational level in response to photoperiodic conditions remained elusive. In this study, we showed that the rice F-box protein FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 (OsFKF1) interacts with and promotes the degradation of the LD-dependent flowering repressor PSEUDO-RESPONSE REGULATOR 37 (OsPRR37)/Heading date 2 (Hd2). Genetic analysis using osfkf1 osprr37 double mutants suggested that OsFKF1 destabilizes OsPRR37 to upregulate Early heading date 1 expression for early flowering under SD. In addition, we found that Hd1, which is a flowering inducer in SD but acts as a flowering repressor in LD, interacts with OsPRR37, suggesting that the Hd1-OsPRR37 complex inhibits flowering under LD. Our results provide new insights into the post-translational regulation of OsFKF1-OsPRR37-Hd1 in photoperiodic flowering in rice.