Identification and gene mapping of the starch accumulation and premature leaf senescence mutant ossac4 in rice

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.