Marker-assisted selection for elevated concentrations of the α′ subunit of β-

Soybean [Glycine max (L.) Merr.] contains two major storage proteins, glycinin and β-conglycinin (BC). Glycinin accounts for approximately 40% and BC approximately 25% of total soybean seed protein (Nielsen et al., 1989). Glycinin is controlled by five genes coding for the acidic (A) and basic (B) subunits: Gy1, Gy2, Gy3, Gy4, and Gy5 (Cho et al., 1989; Nielsen et al., 1989). BC consists of gene families that encode the three major subunits α, α′, and β. The relative concentrations of the BC subunits are about 45% α, 35% α′, and 20% β (Maruyama et al., 1999). Soybean cultivars were discovered by Monsanto Co. with a greater concentration of α′ than α (Bringe and Jenkinson, 2009; Jenkinson, 2009; Jenkinson, 2011). Jenkinson (2009) reported that the cultivars with elevated α′ (EAP) had about 31% α, 40% α′, and 29% β. Soybean cultivars with EAP and elevated BC may enhance the value of soy foods and provide treatment for some health conditions. Rickert et al. (2004) found that soy protein rich in BC has superior gelling properties, improved emulsification, and increased stability. Diets high in BC resulted in lower total cholesterol, triglycerides, and insulin (Aoyama et al., 2001; Moriyama et al., 2004; Yamazaki et al., 2011), showed inhibitory effects on development of atherosclerosis (Adams et al., 2004), and reduced visceral fat related to obesity (Kohno et al., 2006). BC was among the protein components that inhibited the growth of leukemia cells in vitro (Wang et al., 2008) and BC enriched in α and α′ subunits inhibited fatty acid synthase activity reducing lipid synthesis with potential use for cancer treatment (Gonzalez de Mejia et al., 2010; Martinez-Villaluenga et al., 2010). The inheritance of the EAP trait is unknown; however, two Monsanto single nucleotide polymorphisms (SNP) linked to the Cgy2,3 gene associated with the α subunit may be useful for marker-assisted selection (MAS) of the EAP trait (Jenkinson, 2009; Jenkinson, 2011). The two Monsanto SNPs were included in a patent written by Jenkinson (2011) and were claimed to be predictive for the EAP and normal α′ (NAP) traits. Use of MAS for the EAP trait may help reduce the population size required for determining protein composition by sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE), which currently is an expensive and time consuming method. The first objective of this study was to evaluate the effectiveness of the two SNP markers for selecting individuals in segregating populations for the EAP and NAP traits. Japanese scientists developed a soybean line, B2G2, with 0% glycinin and approximately 45% BC concentration (Yagasaki et al., 1996). B2G2 has recessive alleles for the five Gy loci. Jenkinson and Fehr (2010b) used B2G2 in crosses with conventional soybean lines to develop five segregating populations. They derived lines from eight genotypic classes with different combinations of wild-type and mutant alleles at the five Gy loci that were evaluated for protein composition and agronomic performance. Each gy allele affected total BC and glycinin levels differently. They found that the gy1,2 allele had the greatest impact on maximizing total BC and minimizing total glycinin, the gy5 allele was intermediate, and the gy3 allele had the smallest impact. The glycinin genotype gy1,2, gy3, gy4, gy5 had the highest BC concentration and no glycinin. Based on a comparison to a class with all wild-type Gy alleles, they indicated that it should be possible to develop soybean lines with the glycinin genotype gy1,2, Gy3, gy4, gy5 that elevated BC without sacrificing yield, that it would be more difficult to develop high-yielding lines with the glycinin genotype gy1,2, gy3, gy4, Gy5, and the most difficult to develop lines with acceptable yield that have the glycinin genotype gy1,2, gy3, gy4, gy5. They did not evaluate the gene combination of gy1,2, Gy3, gy4, Gy5 to determine how the concentrations of BC and glycinin and the agronomic performance of the lines with that genotype would compare with the glycinin genotypes of gy1,2, Gy3, gy4, gy5; gy1,2, gy3, gy4, Gy5; and gy1,2, gy3, gy4, gy5. The second objective of this study was to evaluate lines with the Gy3 and Gy5 wild-type alleles to determine their impact on agronomic traits and seed composition. No studies have been reported on the impact of the EAP trait on the agronomic traits and seed composition of soybean lines when combined with alleles for modified glycinin concentration. Therefore, the third objective of this study was to evaluate lines with EAP and NAP concentrations combined with the genotypes of gy1,2, Gy3, gy4, Gy5; gy1,2, Gy3, gy4, gy5; gy1,2, gy3, gy4, Gy5; and gy1,2, gy3, gy4, gy5 for the glycinin alleles. Palmitate is one of the major saturated fatty esters in soybean oil averaging 110 g kg¬-1 in conventional cultivars (Wilson, 2004). Soybean oil with elevated palmitate concentration has greater oxidative stability than conventional soybean oil and may be more useful for some food and industrial applications (Shen et al., 1997). Seed from the cultivar Elgin was treated with ethyl methanesulfonate to create the fap4(A24) mutant allele for elevated palmitate concentration (Fehr et al., 1991; Schnebly et al., 1994). Classical genetic studies reported that the fap4(A24) mutant allele segregates independently from all other elevated palmitate mutations (Fehr et al., 1991; Schnebly et al., 1994) and molecular characterization confirmed that the fap4(A24) mutant allele had no mutations in the two Glycinin max 3-ketoacyl-ACP synthase II (GmKAS II) genes (De Vries et al., 2011). The fourth objective of this study was to determine the genetic location of the fap4(A24) locus for elevated palmitate concentration and to identify molecular markers that could be used for MAS of the allele in segregating populations