Studies On Endosperm Amylopectin Structure And Its Association With Quality And Starch Synthesis-related Genes Of Rice

Rice is one of the most important crops in the world.With the development of people's living standard,it is urgent for rice breeders to improve rice quality.For a long time,amylose is considered to be the key determinant of the rice quality.But as the main compositions of rice starch,amylopectin is the determinant of starch granule structure and starch physiochemical properties.Amylose is synthesized by Wx gene and amylopectin synthesis-related genes like SSI,SSIIa,SSIIIa,BEIIb and PUL play an important role on the process of rice amylopectin biosynthesis.So it is necessary to understand the influence of amylopectin structure in starch physiochemical properties and investigate the effect of the starch synthesis-related genes and their alleles to the amylopectin structure and rice quality.That is significant for uncovering the genetic control mechanism of amylopectin structure formation in rice endosperm,and providing the basis for molecular marker assisted selection of rice quality improvement.In this study,the enzymatic method was applied in determining the amylopectin fine structure in rice.The correlations between amylopectin structure and starch physiochemical properties were analyzed.In addition,the molecular markers of sequence polymorphisms in Wx,GS3 and GW5 were validated and developed.The relationship among alleles of these genes and quality and agronomic traits were also analyzed.Further more,the polymorphisms of SSI,SSIIa,SSIIIa,BEIIb and PUL gene among 21 different rice varieties were analyzed.On this basis,association analysis between the polymorphisms of amylopectin synthesis-related genes and amylopectin structure and starch physiochemical properties were performed in order to identify functional alleles of starch synthesis-related genes.The major results were as follows:1.The enzymatic method was applied to characterize the amylopectin fine structure in endosperm of different rice varieties,which contained BV,?-amylolysis,CL,ECL,ICL and A:B.The results of amylopectin fine structures of 91 rice accessions in this study were consistent with the previous reports,which showed that the enzymatic method can be applied to the determination of amylopectin structure in rice.2.The correlations between the amylopectin fine structure and starch physiochemical properties were analyzed.In all rice varieties,CL and ECL showed a positive correlation with HPV?CPV?SBV?PeT?Tp?Te,negative correlation with PKV?BDV and A:B showed a positive correlation with PKV?BDV,negative correlation with HPV?CPV?SBV?PeT?Te.The results showed that chain length distribution of amylopectin was the major factor affecting the gelatinization of starch.The content and proportion of long and short chain determine the rice quality.The amylopectin with higher percentage of long chains,the starch expansion was inhibited;the rice would harder being cooked and had a harder texture,eventually leading to the decline in rice quality.3.For Wx gene,the molecular markers Wx^b,Wx^HH,wx and the number of?AATT?_n in the leading sequence were effective.The rice AC and Wx^b,Wx^HH and the haplotypes composed by them were significantly correlated,and the AC increased as the number of?AATT?_n increased.Furthermore,the two molecular markers for the SNP C/A in Exon 2and the SSR?AT?_n in Intron 4 of the GS3 gene were effective,and all of them showed significant correlation with GL.For the GW5 gene,the STS marker developed by the InDel was effective and significantly correlated with the GW.4.The polymorphisms of five amylopectin synthesis-related genes SSI,SSIIa,SSIIIa,BEIIb,PUL among 21 different rice varieties and their haplotypes were analyzed.The results showed that there were four missense SNPs included two haplotypes in SSI,four missense SNPs included two haplotypes in SSIIa,twenty six missense SNPs included seven haplotypes in SSIIIa,four missense SNPs included five haplotypes in BEIIb,five missense SNPs included four haplotypes in PUL.5.Association test between the starch synthesis-related genes Wx,SSI,SSIIa,SSIIIa,BEIIb and PUL polymorphisms with amylopectin fine structure and starch physiochemical properties were performed.The results showed that all alleles of Wx gene had a significant effect on the rice physiochemical properties of rice,which proved that Wx gene did play a decisive role in rice quality.SS1 gene had a great effect on the physicochemical properties of starch,and had little effect on the structural parameters.The haplotypes of SSIIa gene were significantly different on PaT and structural parameters.Rice varieties with haplotype G/GC had a higher PaT than other haplotypes A/GC and G/TT.So SSIIa was the major gene in regulating gelatinization temperature and forming the amylopectin structure.SSIIIa played a distinct role in the synthesis of long chain of amylopectin in rice endosperm.The different structure could be reflected on the differences in the physiochemical properties and rice quality,suggesting that the four locus of 128,649,691 and 2872 may be the functional polymorphism sites leading to the phenotypic variation.All of the parameters of the haplotype HP2 in BEIIb gene had significant differences with other haplotypes,suggesting that the locu of 346 also may be the functional polymorphism sites leading to the phenotypic variation.The PUL gene also played an important role in the fine structure of amylopectin,and proposed that the 1250 locus may be a very important functional polymorphism site.