Circadian clock confers precise timing of diurnal floret opening in rice
Inter subspecific hybrids between indica and japonica rice have superior heterosis and confer a yield advantage over indica indica hybrids. Nevertheless, their deployment is hindered by differential diurnal floret-opening time (DFOT) between subspecies. Here, we show that rice DFOT is precisely timed by the circadian clock. Through analyses of dissected lodicules, an organ that influences floret movement, we demonstrate that the transcription factor OsCCA1 represses OsAOC and OsMYB8 expression to decrease jasmonic acid accumulation, thereby preventing lodicule swelling and floret opening in the early morning. The evening-phased clock component OsTOC1 activates OsPME11 and OsPME23, promoting homogalacturonan demethylesterification and cell-wall stiffening, preventing floret opening in the late afternoon. A Oscca1 mutant in a japonica cultivar substantially improves floret-opening synchronization with an elite indica male-sterile line, and doubled hybrid seed production under field conditions. These findings resolve circadian-clock regulation of important agronomic traits, and offer practical solutions to enhance indica japonica inter-subspecific hybrid breeding.