Rice FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 (OsFKF1) promotes flowering independent of photoperiod

Abstract

In the facultative long-day (LD) plant Arabidopsis thaliana, FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 (FKF1) is activated by blue light and promotes flowering through the transcriptional and post-translational regulation of CONSTANS under inductive LD conditions. By contrast, the facultative short day (SD) plant rice (Oryza sativa) flowers early under inductive SD and late under non-inductive LD conditions; the regulatory function of OsFKF1 remains elusive. Here we show that osfkf1 mutants flower late under SD, LD and natural LD conditions. Transcriptional analysis revealed that OsFKF1 up-regulates the expression of the floral activator Ehd2 and down-regulates the expression of the floral repressor Ghd7; these regulators up- and down-regulate Ehd1 expression, respectively. Moreover, OsFKF1 can up-regulate Ehd1 expression under blue light treatment, without affecting the expression of Ehd2 and Ghd7. In contrast to the LD-specific floral activator ArabidopsisFKF1, OsFKF1 likely acts as an autonomous floral activator because it promotes flowering independent of photoperiod, probably via its distinct roles in controlling the expression of rice-specific genes including Ehd2, Ghd7 and Ehd1. Like ArabidopsisFKF1, which interacts with GI and CDF1, OsFKF1 also interacts with OsGI and OsCDF1 (also termed OsDOF12). Thus, we have identified similar and distinct roles of FKF1 in Arabidopsis and rice. The F-box protein FLAVIN-BINDING, KELCH REPEAT, FBOX 1 (FKF1) acts as a long day-dependent floral inducer by positively regulating CONSTANS at both the transcriptional and post-translational levels in Arabidopsis. However, the regulatory role of rice FKF1 (OsFKF1) in flowering time remains elusive. Here we show that OsFKF1 acts as an autonomous floral activator independent of photoperiod by modulating the expression of the rice-specific flowering-time genes, Ehd2, Ghd7, and Ehd1.