Submitted to: Crop Science
Publication Type: Review Article
Publication Acceptance Date: November 2, 2003
Publication Date: March 1, 2005
Citation: Krishnan, H.B. 2005. Engineering soybean for enhanced sulfur amino acid content. Crop Science. 45:454-461. Technical Abstract: Soybean is an important protein source in human diets and animal rations. Additionally, human consumption of soybean protein is thought to provide specific health benefits. Since methionine and cysteine contents limit the nutritional value of soybean, efforts involving both traditional breeding and genetic engineering have been employed in an attempt to increase the presence of these essential amino acids. Traditional breeding has been primarily utilized to increase the total protein content, but not to enhance the sulfur amino acid content of soybean. Although mutagenesis in conjunction with traditional breeding is a viable method for enhancing the sulfur amino acid content of soybeans, genetic engineering appears to be a more realistic approach. Introduction of methionine-rich heterologous proteins has resulted in a modest increase of this amino acid in soybean. Elevating the expression of endogenous methionine-rich proteins or introducing synthetic proteins containing a high percentage of essential amino acids are other possible approaches that might increase the nutritional quality of the seed. Even though considerable progress has been made in enhancing the methionine content of soybeans, several obstacles remain. A thorough understanding of the sulfur assimilatory pathway in soybeans is a prerequisite for improving the sulfur amino acid content of the soybean. Expression of feedback-insensitive forms of serine acetyl transferase and O-acetylserine (thiol) lyase, two key enzymes in sulfur assimilatory pathway, should lead to an increase in the availability of sulfur amino acids. An adequate supply of sulfur amino acids in developing seeds may facilitate accumulation of sulfur-rich proteins to a level sufficient to meet the nutritional requirement of livestock and poultry.