OsGRF 4 controls grain shape , panicle length and seed 4 shattering in rice 5

Traits such as grain shape, panicle length and seed shattering, play 36 important roles in grain yield and harvest. In this study, the cloning and functional 37 analysis of PANICLE TRAITS 2 (PT2), a novel gene from the Indica rice Chuandali 38 (CDL), is reported. PT2 is synonymous with Growth-Regulating Factor 4 (OsGRF4), 39 which encodes a growth-regulating factor that positively regulates grain shape and 40 panicle length and negatively regulates seed shattering. Higher expression of OsGRF4 41 is correlated with larger grain, longer panicle and lower seed shattering. A unique 42 OsGRF4 mutation, which occurs at the OsmiRNA396 target site of OsGRF4, seems to 43 be associated with high levels of OsGRF4 expression, and results in phenotypic 44 difference. Further research showed that OsGRF4 regulated two cytokinin 45 dehydrogenase precursor genes (CKX5 and CKX1) resulting in increased cytokinin 46 levels, which might affect the panicle traits. High storage capacity and moderate seed 47 shattering of OsGRF4 may be useful in high-yield breeding and mechanized 48 harvesting of rice. Our findings provide additional insight into the molecular basis of 49 panicle growth. 50 51