| Rice(Oryza sativa L.) is one of the most important food crops all over the world,supporting about 21% of the total caloric intake of the world population. However, in the recent years, with the problems of frequent disasters, an increase of global population, a decrease of cultivated land and rice planting area, food shortage is still a disturbing problem for many countries. Hence, the development of rice genetics and breeding research has become the top priority of agricultural research. Rice yield is a complex agronomic trait determined by polygenes, and it is directly influenced by the the number of productive tillers per plant, grains per panicle and 1000-grain weight. Among them, grain weight is the most important factor, which is controlled by grain filling and grain size. Grain size is composed of grain length, grain width and grain thickness. Besides,grain size is also an important quality trait, people from Southeast Asia usually enjoy rice with long and thin grains while consumers from Northeast Asia prefer short and round rice. As a result, improvement of rice grain is an effective way to increase yield and improve rice quality.In this dissertation, we mainly focus on the research of two grain materials. For the first study, genome-wide genetic map of rice for QTL mapping was constructed with 177 molecular markers in 186 BC1F2 lines derived from the intercross of ’Nipponbare’ and ’T5486’. QTL calculation was performed by QTL mapmaker 3.0 and QTL Network 2.1, and genetic map with 2294.2 c M of total genetic distance, 12.96 c M of average genetic distance between adjoining label was obtained finally. 3 QTLs on 2 chromosomes were found in this study, three of which were detected on the same region, they are q GW12, q GL12 and q GR12. To confirm q GW12, we used BC2F2 population, the gene was finally narrowed into the STS makers of SH78 and SH93, total 6 ORFs have been found in the region. The contribution rate of this QTL is 52.08%, which may conduce the increase of 0.79 mm on grain width and 0.4mm on grain length. Then we used bigger population(BC1F2, BC2F2 and BC3F2) consist by 1861 individuals, it was fine-mapped to an interval of 23.9 kb between STS markers SH78 and SH98, including 3 ORFs.The other material of this study is a BR-related rice mutant, small grain 4(sg4), obtained from callus culture of japonica cultivar Nipponbare. This mutant showed multiple phenotypes such as dark green, rugose erect leaves and small round grains. It was higher than the wild type, different from the majority of BR- and gibberellin-related mutants. Genetic analysis showed that the mutant phenotypes are controlled by a single recessive locus. The gene was fine-mapped to a 90.7-kb interval with 1,100 F2 recessive individuals by means of map-based cloning. Totally 11 open reading frames were found in this interval, only one of which was detected with an 8-bp insertion in the 5’UTR region by sequencing. Functional complementation test revealed that a DWARF11 allele, LOC_Os04g39430, is answer for the mutant phenotype of sg4. Tissue-specific response to BR and decreased expression levels of BR biosynthetic genes suggest that sg4 is a weak BR-deficient mutant. These results are beneficial to understanding the physiological action of sg4 in a more comprehensive way.The study of these two genes supplies a efficiency way to the molecular marker assisted selection on improvement of grain yield and grain quality. The further study of genotype with natural mutation is helpful to analyze the function of diffenrent alleles. It is meaningful to understand the genetic mechanism of the grain size and the realization of the breeding design. |
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