Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2007
Publication Date: 1/1/2008
Citation: Phartiyal, P., Kim, W., Cahoon, R., Jez, J.M., Krishnan, H.B. 2008. The role of 5'-adenylylsulfate reductase in the sulfur assimilation pathway of soybean: molecular cloning, kinetic characterization, and gene expression. Phytochemistry. 69(2):356-364. Interpretive Summary: Soybean is a rich source of protein. Unfortunately, soybean proteins contain low amounts of two important amino acids, methionine and cysteine, that are vital for optimal growth of humans and animals. Therefore, attempts are being made to increase the amount of these two amino acids in soybean proteins. This study reports the cloning and characterization of APS reductase, key enzyme that is involved in the production of cysteine. Our results demonstrate that this enzyme is expressed at very low levels in developing seeds. Since this enzyme plays a major role in the assimilation of sulfur, it is desirable to elevate the expression of this protein during soybean seed development. The information obtained from this basic study will help biotechnologists to genetically manipulate the sulfur-assimilatory enzyme expression levels so that we can improve the overall quality of soybean seed proteins. Superior quality soy proteins can be utilized to meet the nutritional requirements of the multitude of malnourished people around the world.
Technical Abstract: Soybean seeds are a major source of protein, but contain low levels of sulfur-containing amino acids. With the objective of studying the sulfur assimilation pathway of soybean, a full-length cDNA clone for 5’-adenylylsulfate reductase (APS reductase) was isolated and characterized. The cDNA clone contained an open reading frame of 1,414 bp encoding a 52 kDa protein with an N-terminal chloroplast/plastid transit peptide. Biochemical characterization of heterologously expressed and purified protein shows that clone encodes a functional APS reductase. Although expressed in tissues throughout the plant, analysis revealed abundant expression of the gene and activity of the encoded protein in the early developmental stages of soybean seed, which declined with seed maturity. Sulfur and phosphorus deprivation increased expression, while nitrogen starvation repressed APS reductase mRNA transcript and protein levels. Cold-treatment increased expression and the total activity of APS reductase in root tissues. This study provides information on the sulfur assimilation pathway of nutritionally important legume.