Fine Mapping Of Major QTL And Haplotype Analysis Of Candidate Genes For Fatty Acid Components In Soybean

Soybean [Glycine max L.Merr.] contains about 40% protein and 20% oil,which is an important source of edible vegetable protein and oil worldwide.The quality of soybean oil is affected by the fatty acid compositions directly.Therefore,one of most important objectives for soybean quality breeding is to increase the oil content and improve the fatty acid compositions.In this study,we analyzed the contents of oil and fatty acid components,and genetic diversity based on the SSR markers,and explored the domestication characteristics of the oil and fatty acid compositions in various soybean accessions.We also fine mapped the major QTL for fatty acids in the residual hybrid lines(RHLs),and analyzed the haplotypes and association loci of two candidate transcripion factor genes related to fatty acid content in the natural soybean populations,in order to find the functional genes related to fatty acid compositions,which can provide a theoretical reference for quality improvement in soybean breeding.The main findings of this study are as follows:1.The domestication characteristics of the oil and fatty acids in various soybean accessionsIn this study,we analyzed the content of oil and fatty acid components using the NIRs and GC methods,and genetic diversity and domestication characteristics using 32 pairs of SSR markers in 58 soybean accessions.The results showed that there was a significant difference on the oil and fatty acid compositions between wild and cultivated soybeans,which the oil content of cultivated soybean was significantly higher than that of wild soybean.However,regarding to fatty acid compositions,the content of oleic acid in cultivated soybean was significantly higher than that of wild soybean,and on the contrary for the content of linolenic acid.Therefore,we concluded that the content of oil and fatty acid compositions are related with the domestication level in soybean accessions,and the content of oil and linolenic acid maybe use as a reference index for the evolutionary classification in soybean.2.Fine-mapping of major QTL(qLNA20-1)for fatty acid compositionsIn this study,we fine mapped the interval of qLNA20-1 using 26 polymorphic SSR markers and 9 polymorphic SLAF markers in 260 RHL lines based on the ICM-ADD method of ICIMapping software.The results showed that four fine mapping intervals were associated with fatty acid components,including SSR134-SSR130,SSR167-SSR174,SSR9-SSR68,and SSR15-SSR94,with the phenotypic variation explaination of 4.3%-8.17%.The intervals of SSR134-SSR130,SSR9-SSR68,and SSR15-SSR94 were related to the contents of stearic acid,oleic acid,and linoleic acid,respectively,and the interval of SSR167-SSR174 was related to the content of oleic acid and linoleic acid;We found 24 genes in the four fine mapping intervals,including 17 of them annotated in soybean genome.3.Elite Haplotypes and association loci of the candidate genes GmDOF-1 and GmMYB-1We analyzed the whole sequences of the candidate genes GmDOF-1 and GmMYB-1 in 286 soybean cultivars(lines)and found three haplotypes in gene GmDOF-1,including eight SNP and two Indel loci.We found haplotype H1 as the elite haplotype with high stearic acid based on the variance analysis.We also explored the loci of 841-843 and 1336 related to the oil and fatty acids compositions according to the association aanalysis,in which the locus of 841-843 located in the gene coding region can result in an insertion loss of glycine at the level of amino acid.It indicated that the variation of glycine deficiency was the elite hyplotype with high oil content accoding to the variance analysis.For gene GmMYB-1,we found five kinds of haplotype variants,including 14 SNP loci,of which six loci presented in the coding region,in which haplotype H5 was an elite haplotype with high oil and high palmitic acid content.We also explored three loci of 114,198,and 7850 related to the content of oil and fatty acid compositions,of which the locus 7850 causes an allelic variation of phenylalanine and serine at the level of amino acid.It indicated that the haplotype of alanine presented a significantly higher oil content than that of serine according to the variance analysis.