title: Identification of glycinin and beta-conglycinin subunits that contribute to the increased protein content of high-protein soybean lines.
abstract: Seed protein concentration of commercial soybean cultivars calculated on a dry weight basis ranges from approximately 37 to 42% depending on genotype and location. A concerted research effort is ongoing to further increase protein concentration. Several soybean plant introductions (PI) are known to contain greater than 50% protein. These PIs are exploited by breeders to incorporate the high-protein trait into commercial North American cultivars. Currently, limited information is available on the biochemical and genetic mechanisms that regulate high-proteins. In this study, we have carried out proteomic and molecular analysis of seed proteins of LG00-13260 and its parental high-protein lines PI 427138 and BARC-6. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis revealed that the high-protein lines accumulated increased amounts of beta-conglycinin and glycinins, when compared with Williams 82. High-resolution two-dimensional electrophoresis utilizing pH 4-7 and pH 6-11 ampholytes enabled improved resolution of soybean seed proteins. A total of 38 protein spots, representing the different subunits of beta-conglycinin and glycinin, were identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. High-protein was correlated with an increase in the accumulation of most of the subunits representing beta-conglycinin and glycinin. Comparisons of the amino acid profiles of high-protein soybean lines revealed that the concentration of sulfur amino acids, a reflection of protein quality, was not influenced by the protein concentration. Southern blot analysis showed the presence of genotypic variation at the DNA level between PI 427138 and BARC-6 for the genes encoding group1 glycinin, beta-conglycinin, Bowman-Birk inhibitor (BBI), and the Kunitz trypsin inhibitor (KTI). LG00-13260 inherited the allelic variants of the parental line PI 427138 for glycinin, beta-conglycinin, and KTI, while BBI was inherited from the parental line BARC-6. The results of our study indicate that high-seed protein concentration is attributed to greater accumulation of specific components of beta-conglycinin and glycinin subunits presumably mediated by preferential expression of these genes during seed development.
authors.affiliation: Plant Genetics Research Unit, Agricultural Research Service, United States Department of Agriculture, Columbia, Missouri 65211, USA. KrishnanH@missouri.edu
authors.forename: Hari B
authors.initials: HB
authors.lastname: Krishnan
authors.forename: Savithiry S
authors.initials: SS
authors.lastname: Natarajan
authors.forename: Ahmed A
authors.initials: AA
authors.lastname: Mahmoud
authors.forename: Randall L
authors.initials: RL
authors.lastname: Nelson
mesh_terms: D000596:Amino Acids / Q000032:analysis; D052179:Antigens, Plant; D015139:Blotting, Southern; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D005916:Globulins / Q000032:analysis*; D010940:Plant Proteins / Q000032:analysis* / Q000235:genetics; D055314:Seed Storage Proteins; D012639:Seeds / Q000737:chemistry*; D030262:Soybean Proteins / Q000032:analysis*; D013025:Glycine max / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D052179:Antigens, Plant; D005916:Globulins; D010940:Plant Proteins; D055314:Seed Storage Proteins; D030262:Soybean Proteins; C013894:beta-conglycinin protein, Glycine max; C011474:glycinin