D-type cyclin OsCYCD3;1 is involved in the maintenance of meristem activity to regulate branch formation in rice.

D-type cyclins (CYCDs) are involved in a wide range of biological processes, as one of the major regulators of cell cycle activity. In Arabidopsis (Arabidopsis thaliana), three members of CYCD3 subgroup genes play important roles in plant development such as leaf development and branch formation. In rice (Oryza sativa), there is only one gene (OsCYCD3;1) belonging to the CYCD3 subgroup; its function is unknown. In this study, in order to elucidate the function of OsCYCD3;1, we generated knockout mutants of the gene and conducted developmental analysis. The knockout mutants showed a significantly reduced number of branches compared with a wild type, suggesting that OsCYCD3;1 promotes branch formation. Histological analysis showed that the activities of the axillary meristem and the shoot apical meristem (SAM) were compromised in these mutant plants. Our results suggest that OsCYCD3;1 promotes branch formation, probably by regulating cell division to maintain the activities of the axillary meristem and the SAM.