Abstract
Rice Bc6 is a semi-dominant bc mutant with easily breakable plant bodies. In this study, Bc6 gene was cloned by positional cloning. Bc6 encoded a cellulose synthase catalytic subunit, OsCesA9, and has a missense mutation in its highly-conserved region. In culms of Bc6 mutant, cellulose content was reduced by 31%, while hemicellulose content was increased by 48%. Introduction of the semi-dominant Bc6 mutant gene into wild-type rice significantly reduced cellulose content, causing brittle phenotypes. Transmission electron microscopy analysis revealed that Bc6 mutation reduced cell wall thickness of sclerenchymal cells in culms. In rice expressing a reporter construct, Bc6 promoter activity was detected in the culms, nodes, and flowers, and was localized primarily in xylem tissues. This expression pattern was highly similar to that of BC1, which encodes a COBRA-like protein involved in cellulose synthesis in secondary cell walls in rice. These results indicate that BC6 is a secondary cell wall-specific CesA that plays an important role in proper deposition of cellulose in the secondary cell walls.
