The rice mutant ossac4 (starch accumulating 4) was raised from seeds of the rice (Oryza sativa L.) indica maintainer line Xinong 1B treated with ethyl methanesulfonate. The distal and medial portions of the second leaf displayed premature senescence in the ossac4 mutant at the four-leaf stage. Physiological and biochemical analysis, and cytological examination revealed that the ossac4 mutant exhibited the premature leaf senescence phenotype. At the four-leaf stage, the leaves of the ossac4 mutant exhibited significantly increased contents of starch compared with those of the wild type (WT). Quantitative real-time PCR analysis showed that the expression levels of photosynthesis-associated genes were down-regulated and the expression levels of glucose metabolism-associated genes were abnormal. Genetic analysis indicated that the ossac4 mutation was controlled by a single recessive nuclear gene. The OsSAC4 gene was localized to a 322.7-kb interval between the simple-sequence repeat marker XYH11-90 and the single-nucleotide polymorphism marker SNP5300 on chromosome 11. The target interval contained 20 annotated genes. The present results demonstrated that ossac4 represents a novel starch accumulation and premature leaf senescence mutant, and lays the foundation for cloning and functional analysis of OsSAC4.

水稻突变体ossac4（淀粉积累4）从水稻种子升高（水稻L.）籼保持系西农1B用甲磺酸乙酯处理。第二片叶的远端和内侧部分在四叶期的ossac4突变体中显示过早衰老。生理生化分析和细胞学检查表明，ossac4突变体表现出过早的叶片衰老表型。在四叶阶段，ossac4的叶子与野生型（WT）相比，该突变体的淀粉含量显着增加。实时定量PCR分析表明，光合作用相关基因的表达水平被下调，葡萄糖代谢相关基因的表达水平异常。遗传分析表明，ossac4突变受单个隐性核基因控制。该OsSAC4基因定位在简单的序列重复标记XYH11-90和所述目标间隔包含20点注释的基因在染色体11中的单核苷酸多态性标记物SNP5300之间的322.7-kb的间隔。目前的结果表明，ossac4代表一个新的淀粉积累和过早的叶片衰老突变体，并为OsSAC4的克隆和功能分析奠定了基础。