OsGI controls flowering time by modulating rhythmic flowering time regulators preferentially under short day in rice

Abstract

Day length is one of the most important factors that determine flowering time. In this study, we report that a mutation in OsGI reduced the photoperiod sensitivity in rice, resulting in flowering at 91 d after germination (DAG) under short days (SD) and 103 DAG under long days (LD). Transcript levels for flowering regulators that show diurnal rhythmic expression were significantly decreased in the osgi mutants under SD, but chromatin remodeling factor genes were not significantly changed. However, expression by those flowering regulators was not significantly altered in the osgi mutants under LD. Transcript levels for Ghd7 were lower in the mutants compared with the WT before 35 DAG, but higher afterward. These results suggested that OsGI differentially modulates Ghd7 as plants develop. The temporal expression pattern of OsGI was similar under SD and LD. Transcript levels for OsGI peaked at 30 DAG before gradually declining to a minimum at 55 DAG, where they then remained constant until flowering occurred. This developmental regulation of OsGI appears to be the main reason for its affecting photoperiod sensitivity strongly under SD but only weakly under LD.