Identification of a plant introduction soybean line with genetic lesions affecting two distinct glycinin subunits and evaluation of impacts on protein content and composition

Authors: Kim, Wonseok; Gillman, Jason; Krishnan, Hari

Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2013
Publication Date: 8/1/2013
Publication URL: http://handle.nal.usda.gov/10113/57740
Citation: Kim, W., Gillman, J.D., Krishnan, H.B. 2013. Identification of a plant introduction soybean line with genetic lesions affecting two distinct glycinin subunits and evaluation of impacts on protein content and composition. Molecular Breeding. 32(2):291-298.

Interpretive Summary: Soybean seeds are remarkable in that they are used for both human food and the production of soybean oil and soybean meal for animal feed. Soybean seeds possess a high level of protein (~40%) and one class of soybean proteins, glycinins, comprise ~35% of the total. Glycinin proteins are encoded by multiple genes, and though similar, different genes have been found to have different effects on the quality of the soybean protein product tofu. Two of these genes, Glycinin1 and Glycinin4, have negative impacts on tofu quality. In addition, all glycinin proteins have been found to be potential food allergens. For these reasons, there is interest in reducing the level of Glycinin1 and Glycinin4 proteins in soybean seeds. In this work, we report the identification of an exotic soybean line which bears two distinct mutations that prevent accumulation of Glycinin1 and Glycinin4. We also characterize the impacts of these mutations on protein composition and content. We report on the development of molecular markers (DNA-based tools for breeders) which can be used to directly select for these mutations as part of a soybean breeding program. Such molecular tools have the potential to accelerate and simplify the current breeding methods for improved tofu quality.

Technical Abstract: Unlike other oilseeds, soybean (Glycine max [L.] Merr) is also valuable due to its direct conversion into human food. One notable example is the cheese-like product tofu. The quality of tofu is derived from the protein composition of soybean seeds used in preparation, and reduction in protein subunits derived from two glycinin genes, Gy1 and Gy4, is correlated with improved tofu quality. Many superior tofu varieties have been found which feature genetic reductions in glycinin content due to a widespread, naturally-occurring loss of expression mutation affecting one glycinin gene, gy4. Here we report that one exotic soybean plant introduction line has not only the previously described gy4 mutation, but also bears an extremely rare, potentially unique, frameshift mutation (gy1-a) that dramatically reduced Gy1 mRNA accumulation and A1aB1a protein subunit accumulation. Despite the reduction in glycinin content, overall protein levels were unaffected. The novel gy1-a allele was found to be unique in a sampling of 247 diverse germplasm lines drawn from a variety of geographic origins.