Engineering Soybean for Enhanced Sulfur Amino Acid Content

Strategies for increasing methionine and cysteine content of soybeans was discussed in a review paper published in Crop Science. The author discusses the use of traditional breeding methods and genetic engineering attempts to increase these essential amino acids in soybean storage proteins. Traditional breeding methods have not been successful primarily due to the lack of variability in methionine in soybean cultivars. Other researchers have used chemical mutagenesis to alter the sulfur content of soybean protein with limited success, however, the process is not selective and the plants will have several changed traits. While still other researchers have investigated the changing of the ratio of storage proteins in soybeans as a method to improve the quality, or balance, of amino acids. One of the most promising strategies is to engineer soybeans with foreign seed protein that are rich in the sulfur amino acids. These methionine rich proteins are found in other plants (Brazil nut, sunflower, corn) and animal sources (bovine beta-casein). The strategies are defined; research is needed to improve expression of these foreign proteins and to assure that the modified protein will not impact the soybean’s growth and development. The author suggested that a two-prong approach involving metabolic engineering of genes involved in sulfur amino acid synthesis and over expression of genes encoding for synthesis of sulfur-rich storage proteins, may be the most promising way to design soybeans with improved sulfur amino acid levels. This review contained about 80 references on improving sulfur amino acids levels of soybeans.

Krishnan, Hari B. 2005. Engineering soybean for enhanced sulfur amino acid content. Crop Sci. 43: 454-461.