The regulatory network mediated by circadian clock genes is related to heterosis in rice

Exploitation of heterosis in rice (Oryza sativa L.) has contributed greatly to global food security. In this study, we generated three sets of reciprocal F1 hybrids of indica and japonica subspecies to evaluate the relationship between yield heterosis and the circadian clock. There were no differences in trait performance or heterosis between the reciprocal hybrids, indicating no maternal effects on heterosis. The indica-indica and indica-japonica reciprocal F1 hybrids exhibited pronounced heterosis for chlorophyll and starch content in leaves and for grain yield/biomass. In contrast, the japonica-japonica F1 hybrids showed low heterosis. The three circadian clock genes investigated expressed in an above-high-parent pattern (AHP) at seedling stage in all the hybrids. The five genes downstream of the circadian clock, and involved in chlorophyll and starch metabolic pathways, were expressed in AHP in hybrids with strong better-parent heterosis (BPH). Similarly, three of these five genes in the japonica-japonica F1 hybrids showing low BPH were expressed in positive overdominance, but the other two genes were expressed in additive or negative overdominance. These results indicated that the expression patterns of circadian clock genes and their downstream genes are associated with heterosis, which suggests that the circadian rhythm pathway may be related to heterosis in rice.