中文摘要：

小穗发育是决定水稻产量的主要农艺性状，鉴定控制小穗发育的关键基因对研究和分析调控农艺性状的分子机理是至关重要的。本文中，我们鉴定了一组小穗数目明显减少的突变体，命名为decreased spikeleu（des），这里详细研究des2和des5两个突变体。结果显示des2是由单基因隐性位点控制，图位克隆将此位点定位到6号染色体的长臂上，并最终克隆了此基因，发现des2是mocl的一个新的等位突变体。定位克隆和序列分析显示在des5中，LAX基因的编码HLH（螺旋-环-螺旋）结构域的区域发生了一个点突变，暗示des5是lax的一个新的等位突变体。我们的结果暗示小穗和水稻叶腋分枝的发育受相同的遗传途径调控。

英文摘要：

Identification of key regulator genes in the control of spikelet development in panicle, one of the main agronomic traits to determine rice yield, is important to investigate the underlying molecular mechanism and provide the molecular basis for analysis of the agronomic traits. In this study, we have identified a group of mutants with conspicuous reduction of spikelet number, which are designated decreased spikelets （des）. Two of the des mutants, des2 and des＆ were analyzed in detail. We showed that a single recessive locus was responsible for des2 phenotype, which is located on the long arm of chromosome 6. The des2 locus was cloned and it was found that des2 is a new allele of mocl. Positional cloning and sequence analysis showed that there is a point mutation in the HLH do- main-encoding region of LAX gene in des5, indicating that des5 is a new allele of lax. Our data indicate that spikelet development is regulated by the same pathway in the control of development of axillary branches in rice.