QTL Mapping And Candidate Gene Prediction Of Soybean 100-Seed Weight And Quality Traits

In this research,high oil variety Jinong 45 was used as female parent and high protein variety Suinong 76 as male parent.F₂population and its derived F₃generation(F_2:3)were obtained as experimental materials.SNP markers were obtained by Genotyping by Targeted Sequencing technology,and a high-density genetic map was constructed.Combined with 100grain weight,fat and protein content of individual population,QTLs were mapped by composite interval mapping（CIM）,complete interval mapping（ICIM）and interval mapping（IM）,and the physical interval of QTL is determined according to the chromosome physical location information provided by SNP markers.Soybase and Phytozome databases were used to annotate and screen genes in the interval.The main results are as follows:1.The phenotypic data showed that there were significant differences in 100 grain weight,fat content and protein content between the two parents.The absolute values of skewness and kurtosis of fat and protein content in F₂and F_2:3populations were less than 1.The segregation of traits conformed to the normal distribution model and had the genetic characteristics of quantitative traits controlled by multiple genes.There was a stable correlation between agronomic traits and quality traits of the two populations.There was a significant positive correlation between 100 grain weight and protein content,a significant positive correlation between 100 grain weight and fat content,and a negative correlation between protein content and fat content.2.A total of 2399 SNP markers were screened to construct the genetic linkage map.The total distance of the map was 1020.5c M,the average number of markers on 20 chromosomes was 120,and the average length of chromosomes was 51.03c M.Among them,the third chromosome had the largest number of molecular markers（238）,and the 11th chromosome had the longest distance（73.7 c M）.The number of molecular markers on chromosome 20 was the least,with a total of 21,and the shortest distance of chromosome 17 was 25.3c M.The average distance range between SNP markers of 20 chromosomes was 0.14-2.54c M,and the average distance between SNP markers was 0.62c M.3.Based on LOD=2.5,a total of 25 QTLs related to the target traits were mapped in the two populations by three methods,among which the QTL related to 100 seed weight（2020＿q HSW15-1）,protein related QTL（2019＿q PRO11-2）was mapped by three methods;QTL associated with fat content（2019＿q OIL17-1）was located by three methods and could be detected stably in both populations.25 QTLs were distributed on chromosome 3,7,11,12,15,16,17 and 20,including 9 relative major QTLs with contribution rate of more than 10%.A total of 15 QTLs were mapped in F₂population,including 4 QTLs related to 100 grain weight,with a contribution rate of 8.49%-9.01%;5 QTLs related to protein content,with a contribution rate of 3.17%-22.46%;3 QTLs related to fat content,with a contribution rate of 8.67%-17.32%.A total of 13 QTLs were mapped in F_2:3population,including 4 QTLs related to 100 grain weight,with a contribution rate of 0.0035%-10.02%;4 QTLs related to protein content,with a contribution rate of 6.10%-11.84%;2 different QTLs related to fat content,with a contribution rate of 10.45%-26.80%.One QTL related to fat content was repeatedly detected in two populations by three methods,and the loci were stable with high contribution rate.4.5274 genes were found in the 25 QTL mapping intervals.The candidate genes related to100 grain weight,protein and fat were screened by GO annotation.33 candidate genes related to100 grain weight,43 candidate genes related to protein content and 22 candidate genes related to fat content were screened.According to the expression of genes in seeds,21 genes were highly expressed in seeds among the 98 genes,including 8 genes related to 100 seed weight,8 genes related to protein content and 5 genes related to fat content.So these 21 genes are candidate genes for 100 seed weight,protein and fat content in soybean.