中文摘要：

从日本晴背景突变体库中筛选出一个小圆粒突变体small grain 4（sg4），通过一系列BR敏感性测试，发现其表达具有组织特异性．但与传统的BR缺失或不敏感突变体又有所不同．sg4株高增加．解剖学研究表明．SG4能够控制细胞伸长，通过图位克隆和候选基因测序分析，在开放阅读框LOC_Os04g39430．1上的起始密码子前一个碱基处发现8bp的碱基插入．互补实验也证明了LOC_Os04g39430．1即为SG4基因．同时，我们对BR生物合成和信号途径的相关基因进行了表达分析，结果表明，BR生物合成基因和信号调节途径的负调节基因在sg4中的表达量有所降低，而信号调节途径的正调控基因在sg4中表达量升高，表明SG4可以通过某种方式促进正调控因子和抑制BR合成基因的表达来调控BR的生物合成．

英文摘要：

Brassinosteroids （BRs） are important hormones that regulate plant development and physiology. Substantial progresses have been made in BR-related studies, and especially an increasing number of new genes involved in BR biosynthesis have been identified. Here, we characterize a BR-related rice mutant, small grain 4 （sg4）, obtained from callus culture of japonica cultivar Nipponbare. This mutant showed multiple phenotypes such as dark green, rugose erect leaves and small round grains. It was higher than the wild type, different from the majority of BR- and gibberellin-related mutants. Genetic analysis showed that the mutant phenotypes are controlled by a single recessive locus. The gene was fine-mapped to a 90.7-kb interval with 1,100 F2 recessive individuals by means of map-basedcloning. Totally 11 open reading frames were found in this interval, only one of which was detected with an 8-bp in- sertion in the 5rUTR region by sequencing. Functional complementation test revealed that a DWARFll allele, LOC_OsO4g39430, is answer for the mutant phenotype of sg4. Tissue-specific response to BR and decreased expression levels of BR biosynthetic genes suggest that sg4 is a weak BR-deficient mutant. These results are beneficial to understanding the physiological action of sg4 in a more comprehensive way.