| Rice is the main staple food in China. However, the rice quality is commonly poor, despite of their high yield level. Rice qualities are mainly determined by its main component, starch property. Therefore, it is of vital importance to study the physical and chemical characteristics caused by the genes related to the synthesis of starch and the genetic expression and controlling mechanism of these genes, which is the improvement the rice quality via genetic approaches.Rice starch consists of amylose and amylopectin. Both the ratio of the two types of starch and the structure of amylopectin decide the rice qualities. Amylose is synthesized by granule-bound starch synthase (GBSS) encoded by Wx gene, while amylopectin is synthesized by a series of enzymes,including soluble starch synthases,starch branching enzyme and starch debranching enzyme, each of which has different isoforms, so the pathway of amylopectin synthesis is very complex. Recently, there has been much knowledge accumulated about the regulation mechanism of Wx gene as well as its influence on rice quality. However, there have been few such reports on amylopectin. We designed molecular makers on Wx, Sbe1 and Sbe3 loci to detecte the genotype of 53 cultivars, and analyzed the relationship between genotypes and their genetic effects. Furthermore, based on diversity of the genes related to starch synthesis of 13 cultivars which were sequenced, 16 molecular markers were developed to detect the genotypes of 67 japonica cultivars. The statues of genetic composition on 16 gene loci were analyzed. The main results were summarized as following. 1. The molecular markers developed for Wx, Sbe1 and Sbe3 could distinguish indica or japonica alleles at three loci. Among all the 53 rice cultivars, six genotype combinations were observed at Sbe1, Sbe3 and Wx loci, while WxiSbe1jSbe3i and WxiSbe1jSbe3j genotype were absent. In order to explore the genetic effects of three genes, especially for starch branching enzyme genes, ANOVA and multiple comparison analysis were conducted. It showed that rice cultivars with different genotypes exhibited different phenotypes, including amylose content, gel consistency and some of RVA characteristics, and the significant differences were observed. It was concluded that these three genes had randomly recombined during the process of the rice variety development. And the genetic effects of indica and japonica alleles at three gene loci were different. Which, Wx gene plays a major role in determining the starch properties, followed by Sbe1 and Sbe3, and the genetic effects of Sbe1 and Sbe3 in different backgrounds (Wxi, Wxj) are different.2.In terms of genotype on Wx locus, all 67 japonica varieties carry the japonica allele Wxj. While 16 genes related to starch synthesis, no recombination happened in 3 gene loci, and 13 gene loci were replaced by indica alleles with, the frequencies of indica allele introgression by 1.49%-46.27%. Among those genes, SSâ… gene had the highest introgression frequency. It was concluded that those genes related to rice amylopectin had recombined during the process of the rice japonica varieties development. In order to analyze the genetic effects of starch synethesizing genes, step-wise analysis was conducted. The result showed that 7 genes had effects on the 10 physico-chemical properties of rice starch including amylose content; gel consistency; starch RVA characteristic. Isa gene had effects on 5 traits, which were: PKV, BDV, CSV, SBV and PeT. The other 6 genes only had effects on 1-4 traits.The results indicated that the differentiation had been occured on the amylopectin synthesizing genes, and the different alleles function differently. It provided the clue to select appropriate alleles to breed the good quality variety. |
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