Physiological Analysis And Gene Mapping Of Two Novel Leaf Color Mutants In Rice (Oryza Sativa L.)

As the key food crop for more than half of humanity, it is significant to increase paddy rice yield per unit area. Rice genome is small and only about 430 Mb, and this provides insight as model for improving monocots. Inherited mutations have proven to be a valuable system both for gene functional studies and for plant breeder. Of which, "Dwarf breeding" is one of the most famous examples. Innovative breeding methods and the emerging tools of molecular and genome biology as the "Biotechnological tools" must modify the conventional breeding methods and enhance the achievement of rice breeding goals. Pigments are special target in obtaining the electronic energy from the sun and photosynthesis is then conducted. Pigment synthesis is so important that it was paid more and more attention with the development of molecular biotechnology in higher plants. Recently, much interesting results have been obtained by studying chlorophyll-deficient mutants, which lacks one or over certain photosynthetic pigments. Besides its significance in basic studies in chloroplast development, chlorophyll metabolism and photosynthesis, such mutants are also important in breeding, for example, they can be used as a simple marker for genetic purity testing both in hybrid seed production and in CMS line multiplication. In despite of its essentiality and partially productions, compared with abundant mutations in leaf-color characters, much of work was still needed to gain further useful conclusion. Two leaf color mutant were obtained from the progeny of EMS treated seeds of Jinhui10, an excellent restorer line bred in rice institute, southwest university. This thesis reviewed their genetic characters, pigments contents, cell structure, molecular mapping, and etc. The results were as following:1. Identification and molecular mapping of novel leaf color mutant wyv1The wyv1 colored white-yellow leaves at seedling stage and then showed yellow-green at tillering stage, following virescent until to maturity. This mutant decreased chlorophyll contents significantly and the trendline was consistent with chlorotic level. At the seedling stage of showing typical phenotype, chlorophyll fluorescence kinetic parameters were measured and the results showed that coefficient of photochemical quenching (qP), actual efficiency of PSâ…¡(ΦPSâ…¡), electron transport rate (ETR) and initial chlorophyll fluorescence level (Fo), net photosynthetic rate (Pn) and maximum photochemical efficiency of photosystemâ…¡(Fv/Fm) were significantly lower in the severe chlorotic leaf. However, no significant differences were observed for Pn and Fv/Fm between mutational virescent leaf and normal green leaf. To molecular mapping WYV1 gene, XinonglA was crossed with wyv1, the F1/F2 populations were used for genetic analysis and the F2 population was used for mapping. Finally, the wyv1 phenotype was confirmed to be controlled by one single nuclear-encoded recessive gene, and the WYV1 gene was finally mapped between SSR marker Y7 and Y6 on rice chromosome 3. The genetic distance was 0.06 cM and 0.03 cM, respectively, and the physical distance was 84 kb according to indica rice 9311. These results must fascinate the gene cloning as well as its application in breeding.2. Identification and molecular mapping of novel leaf color mutant ygl5The ygl5 displayed stable yellow green leaf during the development, and its total chlorophyll ranged from 1.09 mg g^-1 to 3.11 mg g^-1. As a chlorophyll-deficient mutant, chlorophyll a occupied 66.1% and chlorophyll b occupied 61.2% of that of wild type, respectively. Compared with the wild type, chloroplast structure changed less except of granal stacks. The poor agronomic characters were identified, including effective panicle, plant height, 1,000-grain weight and seed setting rates. Genetic analysis showed that the mutational character was controlled by one major recessive nuclear gene according to F₁ and F₂ population of Xinong1A/ygl5. Four hundreds SSR markers were used for gene mapping and the YGL5 gene was primarily mapped between RM12338 and RM1332, RM3766 on the short arm of the chromosome 3, the genetic distance were 0.9 cM and 5.5 cM,30 cM respectively from the locus. The YGL5 gene was finally mapped between SSR marker SWU3-1 and RM14367 with genetic distances 0.2 cM and 1.9 cM respectively. These provide the basic information for gene cloning and function analysis of YGL5.