Development Of Molecular Markers Of The Starch-Synthesizing Genes And Correlation Analysis Between RVA Profile Characteristics And Quality In Rice (Oryza Sativa L.)

Rice is one of the most important crops in the world that provides staple food for half of the world's population.Starch accounts for about 90%of milled rice,and it is a key determinant of processing,cooking and edible qualities of rice.The demand for superior grain quality,especially cooking and eating quality,has become priority for rice market. Starch is composed of linear amylose and branching amylopectin.It has been widely documented that both the proportion of amylose to amylopectin and the structure of amylopectin are determinants of rice starch texture.Amylose is synthesized by granule bound starch synthase(GBSS).Amylose content(AC) is one of the key determinants to cooking and eating quality,however there existed a very large difference in cooking and eating quality,such as starch viscosity,among cultivars with similar amylose content.The Rapid Visco Analyser(RVA) has been used widely to measure starch viscosity characteristics in cereal,and proved useful in the estimation of rice eating and cooking qualities in rice breeding programs.It may be much precise to select the individuals by using two indices,AC and RVA profile,to determine their eating and cooking quality. amylopectin is synthesized by the co-ordinated actions of soluble starch synthase(SSS), starch branching enzyme(SBE),and starch debranching enzyme(DBE),which consist of multiple types of SSS(SSSⅠ,SSSⅡ,SSSⅢand SSSⅣ),SBE(SBEⅠand SBEⅡ),and DBE [isoamylase(ISA) and pullulanase(PUL)].In addition,several types of these enzymes have multiple isoforms.Although many results have been published related to expression regulation of the Wx gene and its effects on starch quality,more researches are still needed to illustrate the expression regulations of genes involved in amylopectin biosynthesis and their effects on starch quality.The genome sequences available online for both indica (cultivar 93-11) and japonica(cultivar Nipponbare) rice subspecies,polymorphism region is obtained through sequence comparisons of corresponding genes in subspecies indica and japonica rice.Tags of these polymorphism sites play a crucial role in saturation genetic map,map-based cloning,gene function analysis and unveiling genetic polymorphism. Under such a background,gene-tagged markers have been developed for each starch-synthesizing gene,and these markers were used to evaluate roles of starch-synthesizing genes in determining physiochemical properties.Moreover,the relationship between RVA profile characteristics and quality in rice was analyzed.The main results were detailed as following.1.Based upon the subspecies database comparison of indica rice and japonica rice,a total of 15 markers related to starch synthesis were successfully developed,2(RB110, RB120) forAgp gene,6(RB816,RB814,RB815,RB811,RB3828,RB2504) for Sbel gene,3 for Sbe3 gene and 1 for SSIIa,SSIIc,Iso and Pul,respectively.RB 110,RB 120, RB814,RB815,RB3828,RB821,RB822,RB823,RB712 were intron markers;RB816, RB2504,R114/113 were promoter markers.RB811 and RB925 were exon markers. RB924 was the marker located at the 500bp downstream of the 10^th exon of the SSIIa gene.2.Branching enzyme gene markers Sbel and Sbe3 classified the tested materials into 16 genotypes.Agp,SSIIc and Pul gene marker classified the tested materials into 3 genotypes.SSIIa gene marker and Iso Gene marker classified the tested materials into 2 genotypes.3.According to the genotypes classified by the gene markers,analysis of variance was carried out on the differences of the physicochemical property of starch on the 102 samples of non-waxy material.Among the different non-waxy material revealed by the branching enzyme gene,the differences was not significant on the physiochemical characteristics of the starch overall value,suggesting that the influence of these allelic variation of branching enzyme loci revealed by these markers on the starch physicochemical properties of non-waxy rice was not significant,genetic polymorphism revealed by the Agp gene markers correlated significantly with the variations of Hot paste viscosity(HPV),Cold paste viscosity(CPV) and Amylose content(AC),and the materials denoted ab showing the characteristics of relatively high AC.the allelic variation of SSIIc gene(ALk) had significant influence on gelatinization temperature among different rice varieties(gelatinization temperatures:A genotype＜K genotype＜B genotype). 4.A total of 106 rice varieties were employed to study the relationship between RVA profile characteristics and rice quality,including the appearance quality and cooking physico-chemical quality.Results indicated that RVA profiles characteristics had close relationships with chalkiness rate,Chalkiness rate(CR) was positively correlated with Breakdown(BDV) and Setback(SBV) of RVA profile,with correlation coefficients of -0.43** and 0.40**,respectively.RVA profiles characteristics had significant correlation with Amylose content(AC) and Gel consistency(GC) in low amylose content varieties or waxy varieties,while not significant in high or medium amylose content varieties.AC was positively correlated with RVA profiles characteristics except for BDV and SBV of waxy varieties,with correlation coefficients is over 0.85. So,when the less AC is,the more significant correlation with AC and RVA profile in rice.