QTL Mapping Of Hard Seededness In Wild Soybean

It is believed that cultivated soybean[Glycine max?L.?Merr.]was domesticated from annual wild soybean[Glycine soja?Sieb.&Zucc.?].As many of other legume species,hard seededness is a domestication related trait in soybean.Here,by using F₂ and RIL populations developed from cultivated soybean Zhonghuang39 and wild soybean NY27-38,QTLs related with hard seededness were detected.The main results are summarized as followed:1.The cultivated soybean Zhonghuang39 started to imbibe water at two hours,with 74.0%seeds were wrinkle,and reached imbibition at four hours.By contrast,the wild soybean showed 94.0%hard seededness even after 12 hours.Thus the phenotype of individuals in the populations was scored after four hours in water.2.As many as 92.0%F₁ seeds derived from the single F₁ plant remained impermeable after four hours in water,indicating that the hard seededness trait is dominant.In the F₂ population,53 plants showed hard seededness??20%seeds showing imbibition?,155 plants showed continuous distribution?range 20%-80%imbibition?,and 93 plants showed permeable??80%showing imbibition?,which didn?t fit 3:1 genetic ration.These results indicated that the seed-coat impermeability was not controlled by a single gene.In the F₇ population?203 lines?,105 lines showed hard seededness?accounted for51.7%?,45 lines showed continuous distribution?accounted for 22.2%?,and 53 lines showed permeable?accounted for 26.1%?.Besides,seed-coat permeability had some relation with seed coat color and it had no significant relation with seed weight,seed length and seed width.3.Permeable and impermeable individuals in F₂ population were used to construct two DNA pools with equal amount of DNA.These bulks were genotyped with 259 polymorphic SSR markers distributed on 20 soybean chromosomes.A total of 18 SSR markers distributed on chromosome 2 and 6showed polymorphism between the two bulks,with 10 SSR markers located in 16.3 Mb on chromosome 2,and eight SSR markers located in 23.4 Mb on chromosome 6 according to the reference genome.The polymorphic SSR markers were then used to genotype the F₂ population and construct linkage map,two major QTLs were detected by the inclusive composite interval mapping?ICIM?method.QTL on chromosome 2,explaining 17.2%total phenotypic variation,was mapped 276.0 kb genomic region defined by Satt274 and Sat₁98 which containing cloned gene GmHs1-1 and qHS1.The other QTL was mapped on chromosome 6 flanked by BARCSOYSSR₀6₁090 and BARCSOYSSR₀6₁339,which explained 5.3%of the total phenotypic variation.4.When individuals with extreme phenotype in F₇ population were used to construct two DNA pools,a total of 24 SSR markers distributed on three chromosomes showed polymorphism between the two bulks,with 11 SSR markers located in 19.3 Mb on chromosome 2,nine SSR markers located in27.8 Mb on chromosome 6,four SSR markers located in 18.2 Mb on chromosome 3 according to the reference genome.A total of 192 polymorphic SSR markers were used to test a RIL population consisted of 203 F₇recombinant inbred lines.Three QTLs related with hard seededness were detected on Chromsome 2,3and 6,respectively.QTL on chromosome 2 in the marker interval Satt274-Sat₁98,had a R² of 23.3%.The QTL mapped between Sat₂66 and Sat₂36?1.5 Mb?,had a R² of 4.9%.On chromosome 6,the QTL interval was Sat₄02-Satt557?3.8 Mb?,with a R² of 20.4%.These results indicated that DNA pooling strategy is an effective method for tagging QTLs related to hard seededness in soybean.