Modulation of Rice Leaf Angle and Grain Size by Expressing and under the Control of Promoter.

Leaf angle and grain size are important agronomic traits affecting rice productivity directly and/or indirectly through modulating crop architecture. OsBC1, as a typical bHLH transcription factor, is one of the components comprising a complex formed with LO9-177 and OsBUL1 contributing to modulation of rice leaf inclination and grain size. In the current study, two homologues of , and were functionally characterized by expressing them under the control of promoter, which is preferentially expressed in the lamina joint and the spikelet of rice. Increased leaf angle and grain length with elongated cells in the lamina joint and the grain hull were observed in transgenic rice containing much greater gibberellin A (GA) levels than WT, demonstrating that both and are positive regulators of cell elongation at least partially through increased GA biosynthesis. Moreover, the cell elongation was likely due to cell expansion rather than cell division based on the related gene expression and, the cell elongation-promoting activities of and were functional in a dicot species, .