Fine Mapping Of A White Stripe Leaf Mutant St12in Rice

Rice is one of most important crops in the world. Food production largely depends on the ability of photosynthesis, in the purpose of increasing rice production, many important agronomic traits related to photosynthesis has always been hot topics. Chloroplast is the main organelle carries out photosynthesis in the leaf. In-depth study of the regulatory mechanism of chloroplast development and chlorophyll metabolic pathway has important practical significance to the ideal plant type breeding and high light efficiency breeding.We derived a rice leaf color mutant st12from mutant library which used EMS (ethyl methane sulphonate) mutagenized japonica cultivar Wuyujing7. In the2-3leaf stage, the leaf of mutant appeared vertical white stripes, and in the stage of tillering, this trait became more obvious, some leaves even show completely white color, the color of leaves gradually became normal after heading, only with veins and slender white stripes. In this study, We conducted genetic analysis of mutant st12, identified the genetic characteristics of the mutant. We also conducted rough mapping and fine mapping by map-based cloning, and on this basis, predicted candidate genes and preliminary analyzed the gene’s function. The results were summarized as follows:(l)The mutant st12was controlled by a single recessive nuclear gene. We used single seeding plant method, all offspring of mutant st12exhibited the mutant trait, indicating that this trait can stable genetic. Mutants st12was used as female parent, and crossed with indica cultivar TN1, the ratio of normal rice plants to mutant rice plants was3:1in the F2segregated population, genetic analysis showed that the mutant’s characteristic was controlled by a single recessive nuclear gene.(2) The result of electron microscopy indicated that the lamellar structure of chloroplast thylakoid in mutant clearly decreased compared with the wide type, also with disordered arrangement. (3)We used F2population for map-based cloning. ST12was rough positioned on chromosome12long arm between SSR marker RM1246and STS markers YH-1, the physical distance between the two markers was10.5cM. Then we developed six pairs of polymorphisms STS markers for fine mapping, and final mapped this gene in33kb physical distance between two STS markers YH5and YH6. Four genes was predicted in this area, one of them had a function related to phytochrome corresponding, NDPK2. We found a single base deletion by gene sequencing, this change caused protein translation early terminated(4) We also did some physiological experiments to verify the result of sequencing. Temperature gradient experiments showed that the mutant’s phenotype influenced by temperature, under34℃constant cultivation condition, the mutant’s phenotype showed more obvious. Drought and salt stress experiments had proved that the resistance ability of mutant lower than wild-type, may be due to early termination of protein translation result from loss of function, which also verified the result of sequencing.