Fine-mapping Of QPC-8.2 Controlling Rice Brown Grain Protein Content

Rice serves as the main food for human and is one of the oldest crops in Chinese history,which distributes worldwide with diverse characteristics.Currently,more than one third of the world's people consume rice as their staple food.With the advancement of science and technology,people's living standards have gradually improved,and people pay more attention to the rice quality.Grain protein is the second most abundant in rice endosperm,affecting rice eating and cooking quality and serving as the index for evaluating the rice nutrition quality.Therefore,identification QTLs controlling rice protein content will benefit us to develop cultivars with high quality.In the present study,a set of chromosome segment substitution lines(CSSLs)covering the whole genome of rice was employed for identifying QTLs related to brown rice protein content.The CSSLs population was derived from a cross between a japonica cultivar Sasanishiki and an indica cultivar Habataki with Sasanishiki as recurrent parent.SL425,one of CSSLss,exhibits significant higher grain protein content than Sasanishiki.Thus,SL425 was used to cross with Sasanishiki to generate the secondary genetic population for identifying the QTLs responsible for grain protein content.The main results were as follows:1.SL425 shows a significantly higher brown rice protein content than Sasanishiki,which harbors a fragment from Habataki on chromosome 8.Moreover,the remaining fragments are from Sasanishiki.The result indicates that Habataki fragment introgression leads to the increase of the protein content in SL425.Therefore,a QTL named as qPC-8 was inferred to confer the protein content variation.2.SL425 was used to backcross to the recurrent parent Sasanishiki to develop a BC1F2 segregating population.The grain protein content and the marker genotype of this population were measured for further QTL analysis.The QTL analysis indicated that there are two QTLs on the chromosome 8 between marker Z73 and Z120,Z89 and Z3,which were designated as qPC-8.1 and qPC-8.2,respectively.3.In order to narrow the target region of qPC-8.2,more polymorphic molecular markers were developed between markers Z89-Z3.In addition,some individuals with heterozygous genotype in qPC-8.2 target region were selected to generate BC1F3 population for fine-mapping of qPC-8.2.The target region is about 131.07 kb between marker Z24 and Z37.In order to further narrow the target region of qPC-8.2,we developed some polymorphic markers between marker Z24 and Z37,and constructed BC1F4 segregating population.The target gene qPC-8.2 was finally restricted to a region governed by marker ZY-37-ZY-64,and the genetic distance between them is about 68.53 kb.Gene prediction indicates that there are 11 putative ORFs in this region.4.Based on the genotypes of each individual in the BC1F4 segregating population,a contig covering the qPC-8.2 anchored region was constructed,which contains six lines named as L1-6.We investigate the agronomic traits of four lines(L1,L2,L3 and L6)with homozygous genotypes,the results showed that there were no significant differences in number of tillers,length of flag leaf,panicle length,grain number,grain length,grain width,number of primary branches,and 1000-grain weight except heading date and plant height.Moreover,L1 and L2 shows a significantly lower brown rice protein content than L3 and L6.Storage protein components analysis showed that the glutelin contents of L1 and L2 were significantly lower than that in L3 and L6,while the content of albumin,globulin and prolamin were changed,but did not reach the significant level.This indicates that the increase of glutelin content in SL425 is the main reason causing the significant increase of grain protein content.