一个水稻簇生穗突变体的遗传分析与基因定位

水稻的花器官是籽粒形成的基础，对如何提高水稻产量的研究一直都是水稻遗传育种工作者所关注的重点。从一个经EMS诱变的高世代回交群体M2中获得一个簇生穗突变体(Cl)，突变体表型特征为：主穗轴严重退化，枝梗顶端2~4 粒小穗簇生在一起，簇生率高达70%。以粳稻品种日本晴和簇生穗突变体杂交，构建F2群体。遗传分析表明该性状受隐性基因控制，其F2分离比远偏离经典孟德尔遗传分离比。利用该F2群体，采用BSA法将基因定位在4 号染色体的SSR标记CGY-08 与CGY-02 之间，两者间的物理距离为145.7 kb。对该区间内的预测基因测序发现：一个P450 (CYP724B1)基因的第四外显子发生了单碱基的突变，而P450 编码与BR合成相关的蛋白。因此，结合突变体表型和测序结果，推测细胞色素P450可能是控制小穗簇生的候选基因。

Genetic Analysis and Gene Mapping of a Clustered Spikelets Mutant in Rice

Rice floral organ was the foundation of grain formation, and how to improve the yield of rice was the focus of study of rice genetics and breeding workers all the time. A clustered spikelets mutant (Cl) controlled by recessive gene was obtained from a M2 population of advanced backcross populations through EMS mutagenesis. The phenotype of the mutant showed that 2-4 spikelets clustered on the stem of panicle branch with a percentage of clustered spikelets up to 70% and the main axis degraded badly. A F2 population was developed from a cross between a japonica cultivar Nipponbare and the Cl mutant. Genetic analysis indicated that the trait was controlled by recessive gene but the ratio of normal plants to mutant plants in F2 population was deviated from the ratio 3:1. The gene Cl was mapped between SSR markers CGY-08 and CGY-02 on chromosome 4 of rice with a physical region of about 145.7kb by BSA method. Sequencing results of predicted genes in this region showed that there was a base change in exon 4 occurred in a P450 gene named CYP724B1, which encoded proteins related to synthesis of brassinosteroid (BR). Therefore, according to the phenotype of the mutant and sequencing results, the authors speculated that the putative cytochrome P450 was a candidate gene of mutant EMS-Cl.