Gene mapping of starch accumulation and premature leaf senescence in the ossac3 mutant of rice

Leaf senescence is the final stage of plant leaf development. Early leaf senescence leads to a reduction in yield and quality of rice (Oryza sativa). Reduction in yield and quality of rice will cause direct economic losses to farmers, and even insufficient food supply worldwide. Elucidation of the molecular mechanism of premature senescence is important for the genetic improvement of rice. The rice mutant ossac3 (sugar accumulating 3) characterized in this study was raised from seeds of the indica maintainer line Xinong 1B treated with ethyl methanesulfonate. The mutant showed premature leaf senescence associated with excessive starch accumulation in the leaf. Under field conditions, the mutant showed the early senescence phenotype at the seedling stage. Apart from newly developing leaves, the leaves began to turn yellow from the leaf tip extending to the middle of the leaf, and the base of the leaves was pale green. The mutant phenotype was maintained to maturity. Compared to the wild type, photosynthetic pigment content and photosynthetic rate in leaves of the mutant were significantly decreased. Concentrations of reactive oxygen species were significantly increased, antioxidant enzyme activities were significantly reduced, and all analyzed agronomic traits decreased in the mutant. Iodine-potassium iodide staining and starch content analysis showed that starch accumulated in ossac3 leaves. Quantitative real-time PCR analysis revealed changes in the expression levels of starch metabolism-related genes. The mutant phenotype was controlled by a pair of recessive nuclear genes and ossac3 was localized on chromosome 3 between the markers RM15243 and HJY8 with a physical distance of 374.2 kb.