Identification And Gene Mapping Of Rice Early Senescent Leaf (esl3) Mutant

Leaf is an essential organ for photosynthesis. It is one of the core problems of scientific research, followed with extensive interest. Senescence is usually regulated by both genetic information and environment stress, such as nutrition deficiencies, higher/lower temperature and alkali/salt injury and so on (Yoshida et al.,2003). Once senescing, it would extremely influence the traits of crop yield and grain quality, such as seed setting rate and1000-seeds weight. The previous studies suggested that rice would increase yield by approximately2%in theory and1%in practice, when the leave delayed senescence one day at the mature stage. The study of the mechanisms of aging and premature aging of the regulation of gene cloning is an important way to improve the production of rice and other crops. Early senescence mutant is an ideal material studying the molecular mechanism. At present, there have been some early senescence mutants, but most of the research is limited to the study of its gene mapping, physiological characteristics and cell structure and so on. In order to identify and isolate gene regulating leaf senescence in rice (Oryza sativa L.), early senescent leaf mutant esl3, was singled out from the mutant library derived from EMS (ethyl methane sulfonate)-treated seeds of indica rice variety JinhuilO.The mainly results as follows:1The morphological analysis and economical character of esl3The mutant esl3showed senescence from the seedling stage. The middle-upper leaf in mutation displayed a brown and withered phenotype from seedling stage to maturity. Compared with the wild type, panicle number and panicle length were reduced significantly. Grains per panicle,1000-grain weight, plant height and weight of dry matter, were reduced very significantly except for seed setting rate. Further analysis revealed that the panicle length and panicle of the mutant reduced significantly, but the rest internode length were reduced very significantly. There was no significant change in the length of the blade.2Photosynthetic pigment content and Photosynthetic rate of esl3Compared with the wild type, the photosynthetic pigment content declined very significantly in the abnormal leaves. Chlorophyll a, chlorophyll b and carotenoids were down81.5%,90.7%and76%. Photosynthetic pigment content of the green parts increased slightly, respectively by15.3%,6.2%and10.3%. Photosynthetic rate measurements show that the photosynthetic rate of the abnormal leaves was significantly lower than the wild-type, green parts was significantly higher than the wild-type.3Physicochemical analysis of esl3Superoxide anion (O2-) of esl3reduced significantly compared with wild-type, only34.8%of the wild-type. Hydrogen peroxide (H2O2) of esl3increased very significantly, increased45.3%than the wild type. Hydroxyl radical (OH-1) increased nearly doubled. SOD activity of the mutant decreased by40.9%compared with the wild type. POD increased by45.7%. CAT activity decreased significantly, only75.1%of the wild-type.4Ultrastructure observation of esl3Ultrastructural observation was performed and demonstrated that the most cells appeared irregular and void with endolysis and contents pyknotic. Chloroplast of the abnormal leaves appeared that lamellar structure disorganized and thylakoid incorrect.5Fine mapping of ESL3geneGenetic analysis showed the senescence was controlled by a recessive nuclear gene. Using391mutation individuals in a F2generation of Nippomeselesl3, ESL3was mapped between SSR marker RM19085and Indel marker Ind05-2on the chromosome 5with physical distance91kb including14annotated genes. All of these results provide a foundation for the further gene cloning and functional analysis of ESL3gene.