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

Abstract

Flowering time of rice (<i>Oryza sativa</i>) plays important roles in regulating grain yield, quality, and adaptability. <i>O. sativa</i> GIGANTEAN (OsGI), heading date 1 (Hd1), and <i>O. sativa</i> 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 26<i>S</i> proteasome. OsFKF1 is functionally conserved with FKF1 in <i>Arabidopsis</i>. Mutations of <i>OsFKF1</i>, <i>OsGI</i>, and <i>Hd1</i> generated through CRISPR-Cas9 in the same genetic background confer late flowering phenotypes. The <i>osfkf1</i> mutations suppress the expression of <i>Ehd1</i>, <i>Hd1</i>, and <i>Ehd2</i>, while activating <i>Ghd7</i> and <i>Ehd3</i>, which further reduces the expression of florigen genes <i>Hd3a</i> and <i>RFT1</i>, leading to delayed flowering time. Mutations of <i>OsFKF1</i> 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.