Identification Of Oil Content QTL In Brassica Napus L. By GWAS And EQTL Analysis

Brassica napus L.(Brassia napus,AACC,2n=38)is an important oil crop in China.The total amount of rapeseed oil plays an important role in meeting the demand of edible oil in China.Increasing the oil content of rapeseed is one of the effective methods to increase the total amount of seed oil.The identification of oil content QTLs and candidate genes of rapeseed are the basic work to reveal the formation and accumulation mechanism of rapeseed oil,which is very important for the improving of oil content of rapeseed.In recent years,the rapid development of sequencing technology and multi-omics research have made it possible to apply high-density markers and multi-omics integration strategies in the identification of oil content QTLs.In order to identify oil content QTLs and candidate genes,and provide a reference for the breeding of high oil content rapeseed,in this study we resequencing 495 representative rapeseed lines,and combined with high density marker to conduct GWAS(Genome Wide Association Study)of oil content,and at the same time,eQTL(Expression Quantitative Trait Locus)analysis was performed using gene expression data and genotype data of 309 materials of the Brassica napus populations.The main findings are as follows:In this study,we investigated the oil content of Brassica napus populations in multiple environments.It was found that the oil content of individuals in the same environment was quite different.By resequencing the 495 materials,8,756,395 high-quality SNPs were identified in this study and the density of SNPs is 13.5 SNPs/Kb.210,356 SNPs were selected for phylogenetic tree construction and population structure analysis.The population structure analysis showed that the population can be divided into three subgroups,of which the P1 subgroup contains 180 materials,the P2 subgroup contains 108 materials,and the remaining 207 materials belong to P3 subgroups.We analyzed the LD(Linkage Disequilibrium)attenuation distance of the A/C subgenome.The corresponding linkage disequilibrium attenuation distances of the A/C subgenome were 72.3 Kb and 995.5 Kb,respectively.By performing the genome-wide association analysis,we identified 37 significant oil content QTLs.The phenotypic variation explained by each QTL range from 0.25% to 10.53%.Twenty QTLs were located in the interval of the reported QTLs,and the remaining 17 QTLs were newly identified in the study.Of the 37 significant QTLs,7 QTLs can be detected in multiple environments,while the remaining 30 QTLs can only be detected in a single environment.Base on the results above,we further identified three stable oil content QTLs of Brassica napus,which were located on the A05,A07 and A09 chromosomes,respectively.By integrating the information of significant SNP and Arabidopsis gene,we identified four candidate genes in two intervals on A05 and A09 chromosomes.Finally,we used the gene expression data of 309 rapeseed individuals for eQTL mapping analysis,81,068 cis eQTLs and 137,984 trans eQTLs were identified,and 30 trans eQTL hotspots were identified based on the results above.By integrating the results of GWAS and eQTL mapping,we found that 1,360 significant eQTL were located within the oil content QTLs,including 435 trans eQTLs and 925 cis eQTLs.Of these,41 eQTLs were significantly associated with oil content phenotypes,including 9 trans eQTLs and 31 cis eQTLs.