The Role of OsELF3-1 in Flowering-Time Control Has Differentiated During Evolution of Rice

EARLY FLOWERING 3 (ELF3) is a circadian clock component, which functions not only as the night time repressor for a set of clock gene expression but also as a modulator to reduce light sensitivity during night. In Arabidopsis, elf3 mutant strongly affects the expression of circadian clock genes, such as GI and PRRs, resulting in a photoperiodic flowering defect. In rice, there are two ELF3 homologs in its genome, namely OsELF3-1 and OsELF3-2. Survey of OsELF3-1 among monocot genome indicated that OsELF3-1 is a rice specific gene, which is recently duplicated from the evolutionarily conserved OsELF3-2. Although loss of both OsELF3-1 and OsELF3-2 is required for strong derepression of OsGI and OsPRRs expression during night, we found that only oself3-1 knock-out is sufficient for delaying flowering remarkably under long-day with an increased expression of Ghd7. Ghd7 is the floral repressor regulated through a gated phytochrome signaling. However, oself3-1 strongly affects neither the expression of rice circadian clock genes, OsGI and OsPRRs nor the peak timing of red-light sensitivity, indicating that OsELF3-1 represses Ghd7 expression independently of circadian clock. In addition, oself3-1 suppressed the red-light insensitive phenotype of se5, a chromophore deficient mutant, leading to derepression of Ghd7 and suppression of early flowering of se5. Taken together, our results imply that OsELF3-1 has functionally diversified during evolution of rice and gained the ability to regulate phytochrome signaling independently of circadian clock regulation.

This work was supported by the MAFF (IVG3005, GMO1005 and GPN0001) and JSPS (23687007).