Variability Analysis Of Protein Subunits Of Chinese Soybean Germplasm

Soybean[Glycine max(L.) Merr is one of the important resource of vegetable protein for human food,and the protein is rich with essential amino acids for human bodies.11 S,7S and their subunits (α、α’、β、A3.A1A2A4,B) are important traits of soybean protein. Several studies have been done on protein content and 11S/7S by QTL mapping,but less concern is on relative content of α、α’、β、A3、A1A2A4,B.The traditional QTL studies mainly focus on the content of protein, and use separate groups of mapping. As a result of the separation of groups that involved only two specific materials, linkage analysis involves only two alleles of the same position. In recent years, association analysis improve the accuracy of QTL mapping. This research can obtain more precise QTLs of soybean protein subunits through the method of combining linkage analysis with association analysis. This study will provide new opportunity to molecular assisted selection breeding for soybean protein.The main objectives of this study are:1) with Chinese soybean mini core collections analyzing variation characteristic of all subunits and 11/7S in different eco-regions in China utilization of soybean germplasm resources, exploring the protein subunit and 11S/7S, and screening out elite accessions for breeding purposes.2) Mapping QTLs of protein subunits and 11/7S with the RIL of (ZDD09454) x Yudoul2, and protein subunit and 11S/7S QTLs by both association analysis and linkage analysis, in order to obtain accurate QTLs and provide valuable guidance in soybean protein quality breeding.The main results obtained in this study are as follows:1) As the mini core collection has high genetic diversity, it is the best candidate material for screening the favorite trait, the CV of α’、α、β、A3、A1A2A4、11S/7S are 0.410、0.330 0.311、 0.211、0.123、0.170 and 0.400. The relative content of subunits and variance degree are different among different ecological regions, variance characteristic and direction are different too. Overall, the relative content of A1A2A4、B、11S/7S of Ⅰ G.max(0.220.0.403、 2.616) is higher than II G.max(0.212、0.370.2.343); the degree of variance of α’、β、 A3、A1A2A4 of I.G. max (0.549、0.270、0.259、0.193) is higher than Ⅱ Gmax(0.435、0.262、 0.254、0.185), a、B、11S/7S of I G. max(0.333、0.184、0.249) is lower than Ⅱ Gmax(0.348、 0.216.0.331).2) The results show that the high variation extent of 7S subunits is the main reason that causes the 11S/7S ratio variance. Fewer loci are detected to be associated with the protein subunits whose phenotypic variation is higher, which might be due to the more recombination incidents during the evolution of the related genes. Therefore the LD decay distances of these genes are short, and some QTLs cannot be detected with limited SSR markers. The results of this study are meaningful for the marker assisted selection breeding of soybean varieties with higher protein quality.3) By combining linkage analysis with association analysis, we obtain two important QTL loci, one associated with A1A2A4 subunit from Satt481 and Satt313 in the L linkage group, and another associated with B subunit which is during BE801128 and Satt477 in the O linkage group. These loci provide valuable guidance for molecular assisted breeding.