|Matthews, Benjamin - Ben|
Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/1999
Publication Date: N/A
Interpretive Summary: Soybeans are a major crop in the United States and world wide. A principle use of soybean in the U.S. is meal for animal feed. The level of the essential amino acid, methionine, is low in soybean meal. Farmers supplement soybean meal with methionine, which represents an added cost to the farmer and to the consumer. Increasing the level of methionine in soybean through breeding and through molecular techniques could decrease farmer and consumer costs. The enzyme, cystathionine gamma synthase, is the first enzyme of the pathway committed solely to methionine synthesis. Little is known about its regulation and expression. We have cloned a cDNA encoding soybean cystathionine gamma synthase and demonstrated its function by complementing a bacterial auxotroph, Escherichia coli AB301, lacking cystathionine gamma synthase activity. This cDNA and information is important to scientists and breeders interested in modifying the pathway leading to the synthesis of methionine in soybean and other crops to increase methionine production.
Technical Abstract: Methionine is one of the essential amino acids that is synthesized in low amounts in seeds of many agronomically important crop plants. The seed protein of these plants, including soybean, is used as animal feed which is low in methionine. Cystathionine-gamma-synthase is the branch point enzyme leading to methionine synthesis. It catalyzes the conversion of o-phospo-homoserine and cysteine to cystathionine. We isolated a cDNA containing a single open reading frame of 1609 bp from a leaf cDNA library. The reading frame encodes a protein of 536 amino acids having a predicted molecular mass of 58, 090 daltons. The amino terminal portion of the deduced amino acid sequence contains a putative chloroplast transit peptide of 153 amino acids. The soybean cystathionine-gamma-synthase amino acid sequence shares sequence identity with that from Arabidopsis and corn. The mRNA was most abundant in light-grown tissues. A construct containing the coding region lacking the transit pepetide was made and transformed into an E. coli auxotroph lacking cystathionine-gamma-synthase. The complemented auxotroph grew normally without methionine supplementation. This information is important to scientists interested in genetically engineering or breeding soybean and other crops to produce more methionine.