CONSTANS-like 9 (COL9) delays the flowering time in Oryza sativa by repressing the Ehd1 pathway

•CONSTANS-Like 9 (OsCOL9) is a constitutive repressor to delay flowering time in rice by repressing the Ehd1 pathway.•OsCOL9 served as a potential yield gene to increase the grain number of main panicle.•OsRACK1 responded to the change of daylight, and associated with OsCOL9 to act upstream of Ehd1.

Flowering or heading is one of most important agronomic traits in rice. It has been characterized that CONSTANS (CO) and CONSTANS-like (COL) proteins are critical flowering regulators in response to photoperiodic stress in plants. We have previously identified that the COL family member OsCOL9 can positively enhance the rice blast resistance. In the present study, we aimed to explore the functional role of OsCOL9 in modulating the photoperiodic flowering. Our data showed that overexpression of OsCOL9 delayed the flowering time under both short-day (SD) and long-day (LD) conditions, leading to suppressed expressions of EHd1, RFT and Hd3a at the mRNA Level. OsCOL9 expression exhibited two types of circadian patterns under different daylight conditions, and it could delay the heading date by suppressing the Ehd1 photoperiodic flowering pathway. In contrast, the expressions of previously reported flowering regulators were not significantly changed in OsCOL9 transgenic plants, indicating that OsCOL9 functioned independently of other flowering pathways. In addition, OsCOL9 served as a potential yield gene, and its deficiency reduced the grain number of main panicle in plants. Furthermore, yeast two-hybrid assay indicated that OsCOL9 physically interacted with Receptor for Activated C-kinase 1 (OsRACK1). Rhythmic pattern analysis suggested that OsRACK1 responded to the change of daylight, which was regulated by the circadian clock. Taken together, our results revealed that OsCOL9 could delay the flowering time in rice by repressing the Ehd1 pathway.

Graphical abstractWe have previously identified that the COL family member OsCOL9 can positively enhance the rice blast resistance. In the present study, we aimed to explore the functional role of OsCOL9 in modulating the photoperiodic flowering. OsCOL9 delayed the rice heading through repressing the Ehd1 pathway under both SD and LD conditions. In addition, OsRACK1 interacted with OsCOL9 in response to circadian photoperiod, which probably mediated the OsCOL9 degradation and played an important role in regulation of rice flowering.Figure optionsDownload full-size imageDownload high-quality image (83 K)Download as PowerPoint slide