Mutation of rice bc1 gene affects internode elongation and induces delayed cell wall deposition in developing internodes

A rice COBRA-like gene, BRITTLE CULM1 (BC1) has been shown to be involved in assembling cell wall components and cellulose crystallinity, which determines mechanical strength in above ground organs. However, the detailed roles of BC1 in rice development are poorly understood. In this study, we found that, unlike the known brittle culm mutants, the internode length of the bc1 mutant was ~1.27 times longer than that of wild type in rice. In order to analyze the effects of bc1 mutation on internode development, we compared the deposition of cell wall components among each developmental stage of the elongating second internodes from wild type, Kinmaze, and the bc1 mutant. In wild type, histochemical observations of lignin revealed that lignin deposition was gradually increased after the cell elongation stage of the internodes. Cellulose and p-coumaric acid (pCA) content also gradually increased along with the progress of the developmental stage. The ferulic acid (FA) content rapidly increased in the cell elongation stage and decreased at the late secondary cell wall formation stage. In the bc1 mutant, the contents of cell wall components were lower than those of wild type from the cell elongation stage, in which the BC1 started to express at this stage in wild type. In the bc1 mutant, the deposition patterns of cell wall components, especially phenolic components including lignin, pCA, and FA, were delayed compared with those of wild type. These results suggest that the BC1 gene plays a role in synthesizing appropriate cell walls at each stage in the developing internode.