Several brittle culm mutants of rice were identified and characterized. In this study, we characterized a brittle mutant （bc7（t）） identified from japonica variety Zhonghua 11 by means of ^60Co-γ radiation. This mutant displays normal phenotype similar to its wild type plants except for the fragility of all plant body, with - 10% decrease in the cellulose content. The genetic analysis and gene fine mapping showed that the bc7（t） mutant was controlled by a recessive gene, residing on an 8.4 kb region of the long arm of chromosome 1. The gene annotation indicated that there was only one putative gene encoding cellulose synthase catalytic subunit （CesA） in this region, which was allelic to OsCesA4. Furthermore, the sequence analysis was carried out and 7 bases deletion in the junction of exon 10 and intron 10 was done in bc7（t） mutant, resulting in the change of reading frame and the consequent failure to generate functional protein. In addition, the result of RNA interference experiment showed that when the Bc7（t） was knocked down, the transplants exhibited fragility, similar to bc7（t） mutant. The finding of novel allele of OsCesA4 locus will facilitate the understanding of the mechanism of cell wall biosynthesis. The potential utilization of the bc7（t） mutant in animal food was discussed as well.
