| Brassica napus L.(Rape)is one of the most important oil crops in the world.Rapeseed oil is widely used in the hands of food processing,clean fuel and industrial production by right of the diversity of fatty acid composition.Chinese limited planting area of rape and the urgent needs of production make improving fatty acid composition of rapeseed oil one of the main tasks of rape breeding.Therefore,based on the digging out mechanism of fatty acid metabolism and exploring appropriate candidate genes,this study was done in rape.In this study,the high generation recombinant inbred lines(RILs)were used as experiment materials,which were derived from synthetic 10D130 and conventional variety Zhongshuang11,and field experiments were conducted in 2016-2017 and 2017-2018 with two different environments in Beibei District of Chongqing City,respectively.After self-pollinated seeds were harvested each year,fatty acid components of seeds were measured by GC with three technical repeats.Then,the RIL population genotype was analyzed with the rapeseed 6K SNP chip array.The SNP linkage map was constructed by using Join Map 4.0 program with minimum LOD 2.0.Quantitative trait loci(QTL)mapping of main fatty acid composition was conducted by composite interval mapping using software Windows QTL Ici Mapping V4.1.Finally,three materials with different fatty acid composition in grains were selected on the 25 th day after anthesis and used in the transcriptome sequencing and analysis.Then the fatty acid metabolism mechanism of rape was deeply analyzed,and some important candidate genes were identified.The main results and conclusions are as follows:(1)Construction of high density genetic linkage map: Though the genotype for 186 lines of RIL population using the 6K rape SNP chip,a high-density genetic linkage map containing 1897 SNP markers was constructed.The genetic map covered 3214.19 c M of rape genome,with the covering length as 1746.27 c M of A genome and 1467.92 c M of C genome,respectively.And the average genetic distance between adjacent markers was1.69 c M,proved that the efficiency and precision in QTL detection were high.(2)QTL mapping of main fatty acid content in rape: In two environments,the difference of six fatty acids in RIL population was significant or extremely significant,and the characters were continuously distributed in the two environments,proved that the material was suitable for QTL detection.Six QTLs were found related to stearic acid content,three QTLs related to oleic acid content,four related to linoleic acid,five related to linolenic acid,two related to eicosenoic acid and three related to erucic acid by using the map.A total of 23 QTLs were detected and distributed on A01,A02,A05,A08,A09,A10,C03 and C07 chromosomes,among which QTL "enriched regions" of fatty acid were found on A05,A08 and C03 chromosomes,and four major QTLs(q A08ST-1,q A05 LI,q C03LI-1,q C07LN)were newly identified by RIL population.(3)Partly genetic basis for competitive disequilibrium of two metabolic pathways downstream of oleic acid: According to the phenotypic correlation analysis and QTL correlation analysis,it was found that the two major QTLs for erucic acid content on A08 and C03 chromosomes were also the main loci of oleic acid content,while the major QTLs for linoleic acid content on A05 chromosome were only the minor loci for oleic acid.The major QTLs for erucic acid content on A08 chromosome were also those of linoleic acid content,while the major QTLs for linoleic acid content on A05 chromosome were not those of the QTL of erucic acid content,which couldn’t explain the phenotypic variation of erucic acid content.The results revealed the unbalanced competition of the two metabolic pathways downstream of oleic acid,which proved that the "carbon addition" pathway had more advantages than the "dehydrogenation" pathway-the former restricted the content of linoleic acid,while the latter had little effect on the content of erucic acid.(4)Key candidate genes identified by QTL and transcriptome sequencing: By anchoring the marker information of fatty acid content QTL interval on the whole genome in rape,Darmor,the differentially expressed genes of each QTL interval were determined and the genes of rape were annotated with Arabidopsis gene function.Then the candidate genes with differentially expression related to oil metabolism were selected and nine key genes were obtained,including Bna A02g01770 D,Bna A05g25110 D,Bna A05g25260 D,Bna A05g26900 D,Bna A08g11130 D,Bna A10g13450 D,Bna C03g65000 D,Bna C03g65980 D and Bna C03g68310 D.These genes were predicted to regulate the biosynthesis and metabolism of oil mainly by encoding diacylglycerol acyltransferase,fatty acid desaturase,fatty acid extender,phosphatidylate phosphatase and involving in acyl Co A biosynthesis. |
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