An F-box protein OsFKF1 interacts with either OsGI or Hd1 and mediates the degradation of OsGI to control flowering time in rice.

Flowering time of rice (Oryza sativa) plays important roles in regulating grain yield, quality, and adaptability. O. sativa GIGANTEAN (OsGI), heading date 1 (Hd1), and O. sativa flavin-binding, Kelch repeat, and F-box 1 (OsFKF1) are key factors controlling flowering time in rice. However, their relationships are not quite clear. In this study, we found that OsFKF1, an F-box domain-containing protein, physically interacts with OsGI and Hd1. OsFKF1 targets OsGI for degradation through ubiquitination-mediated 26S proteasome. OsFKF1 is functionally conserved with FKF1 in Arabidopsis. Mutations of OsFKF1, OsGI, and Hd1 generated through CRISPR-Cas9 in the same genetic background confer late flowering phenotypes. The osfkf1 mutations suppress the expression of Ehd1, Hd1, and Ehd2, while activating Ghd7 and Ehd3, which further reduces the expression of florigen genes Hd3a and RFT1, leading to delayed flowering time. Mutations of OsFKF1 also affect the agronomic traits and enhance grain yield. These findings reveal the molecular mechanisms of OsFKF1 on regulating flowering time and provide valuable germplasm resources for rice breeding to improve growth period.