OsKRP3 plays important role in cell cycle control during the early stage of rice endosperm development. OsKRP3 determines the final number of endosperm nuclei and the final seed size by regulating cell cycle arrest at the end of the syncytial phase (Mizutani et al., 2010). Yeast two hybrid results showed that OsKRP3 interacts with OsCDKA;1, OsCDKA;2, OsCycA1;1, and OsCycD2;2, thus has ability to inhibit rice CDK and to change the cell size. Strong expression of OsKRP3 was observed in the multinucleate syncytium at 2 DAF (days after fertilization) and that its expression was significantly reduced after cellularization (Mizutani et al., 2010).