Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2006
Publication Date: 3/7/2007
Citation: Krishnan, H.B., Natarajan, S.S., Mahmoud, A.A., Nelson, R.L. 2007. Identification of glycinin and beta-conglycinin subunits that contribute to the increased protein content of high-protein soybean lines. Journal of Agricultural and Food Chemistry. 55(5):1839-1845. Interpretive Summary: Soybeans, which provide 67% of the vegetable protein and 30% of vegetable oil, are an integral link in the world food chain. Continued improvement in the performance of this crop is vital if increased demand for food by a burgeoning world population is to be met. Presently, soybeans grown in the United States have an average protein content of 40% but shifts in production to the upper Midwest and continued emphasis on breeding for yield rather than quality threatens to lower this percentage of protein. Development of high-protein soybean lines will facilitate cost efficient production of high protein meals containing at least 48% protein. Currently, limited information is available on the biochemical and genetic mechanisms that regulate high seed protein concentration. In this study, we employed various analytical methods to determine whether the high protein lines preferentially accumulate specific proteins and to compare the relative accumulation of amino acids in the high protein lines. Our data provides increased knowledge of the variability of protein and protein subunit accumulation among high protein cultivars which will facilitate ongoing efforts to improve both the quantity and quality of soybean seed protein. Increased protein quality will benefit the overall utilization of soybean in the food and feed industries.
Technical 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. 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-protein. 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 to 7 and pH 6 to11 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 the beta-conglycinin and glycinin. Comparisons of the amino acid profiles of high-protein soybean lines revealed 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, BBI and KTI protease inhibitors. 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.