Identification of several gy4 nulls from the USDA soybean germplasm collection provides new genetic resources for the development of high-quality tofu cultivars

Tofu, a cheese-like food made by curdling soy milk, is a major dietary staple of Asian countries. Consumption of tofu and other soy products is steadily increasing in North America due to its well-known health benefits. Soybean A₅, A₄, and B₃ peptide null lines 'Enrei? and 'Raiden? are commonly utilized in breeding programs to develop high-quality tofu cultivars. To expand the genetic diversity it is desirable to identify and utilize other A₅, A₄, and B₃ null genotypes in the development of improved tofu cultivars that are adapted to North American conditions. In this study were screened diverse soybean accessions from the USDA Soybean Germplasm Collection to identify Gy4 mutants, the locus that controls A₅, A₄, and B₃ peptide production. Analysis of total seed proteins from 485 soybean lines by SDS-PAGE enabled the identification of 38 accessions that lacked the A₅, A₄, and B₃ peptides. These accessions showed marked differences in seed size and seed coat color and represented different maturity groups ranging from 0 to IX. To ascertain the molecular basis for the lack of A₅, A₄, and B₃ peptides in the newly identified Gy4 mutants, the nucleotide sequence of a portion of the Gy4 gene was determined from eight soybean accessions representing different maturity groups. These eight Gy4 mutants revealed a single point mutation that changed the translation initiation codon ATG to ATA, resulting in the A₅, A ₄, and B₃ null phenotype. The newly identified Gy4 mutants from this study will enable plant breeders to expand the genetic diversity of North American food-quality soybeans and also aid in the development of hypoallergenic soybeans.