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.
The property of starch in rice grain endosperm is a very important determinant for rice quality, and it is essential to understand the genetic effect of the genes related to starch synthesis in high-yielding rice varieties for rice quality improvement. The physicochemical properties （e.g., amylose content, gel consistency, and RVA profile） were assessed on 53 rice varieties, including certain typical indica/japonica landraces and certain high-yielding modern varieties. And molecular markers for Sbel, Sbe3 developed on the basis of sequence diversities between the rice subspecies indica and japonica, together with PCR-Acc I marker for Wx gene were used to investigate the genotypes of 53 rice cultivars. The result showed that the developed molecular markers for Wx, Sbel, Sbe3 could distinguish indica or japonica alleles at three loci. Among all the 53 rice cultivars, six genotypes were observed when Sbel, Sbe3, and Wx loci were considered together, while the genotypes of WxiSbelJSbe3i and WxiSbelJSbe3J were absent. In order to explore the genetic effects of the three genes, especially for starch branching enzyme genes, ANOVA and multiple comparison analysis were conducted. The results showed that rice cultivars with different genotypes exhibited different phenotypes, including amylose content, gel consistency and certain RVA characteristics, and the significant differences among the six genotypes were observed. It was concluded that these three genes had randomly recombined during the process of the rice variety development. And the genetic effects of indica and japonica alleles at three gene loci were different, of which, Wx gene plays a major role in determining the starch properties, followed by Sbel and Sbe3, and the genetic effects of Sbel and Sbe3 in different backgrounds （Wx~, WxJ） are different. The results have provided a clue for rice good quality variety development, and the molecular markers will benefit to the improvement in quality of rice.
YAN Chang-jieTIANShunZHANG Zheng-qiuHAN Yue-pengCHEN FengLI XinGU Ming-hong
