Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 18, 1999
Publication Date: N/A
Interpretive Summary: Corn and soybeans are the two most important crops in the United States. They are used directly as food sources for humans as well as providing forage for livestock. Although they are high in protein each is deficient in its amino acid content. As a result amino acids must be added to soybeans to make a complete protein source for animals and humans. We cloned a soybean gene encoding an important enzyme, aspartokinase. This is the first enzyme dedicated to the syn synthesis of three important amino acids, lysine, threonine, and methionine. We determined its DNA sequence and studied the regulation of the gene in soybean to determine when it is expressed and at what levels. This work is of interest to soybean scientists trying to genetically engineer soybean to produce more lysine, threonine, and methionine.
Lysine, threonine, and methionine are essential amino acids required in the diets of humans and nonruminent animals. The first enzyme in the pathway leading to the synthesis of these amino acids is aspartokinase. We isolated a cDNA encoding a lysine-sensitive aspartokinase (AKL) from soybean (Glycine max). This clone has high sequence similarity to two Arabidopsis sequences coding for AKL. Unlike previous soybean clones that were shown to encode bifunctional aspartokinase-homoserine dehydrogenases, this clone encodes a monofunctional aspartokinase. The clone encodes a putative transit peptide and suggests that AKL is localized to the chloroplast. Northern blots of mRNA isolated from soybean seedlings grown in the dark and light indicate a single band of 2.25 kb when hybridized to the clone encoding AKL. The transcript was most abundant in light-grown tissues. This information is useful to scientists interested in genetically engineering soybean to produce more of the essential amino acids, so farmers will not have to supplement meal for optimal growth of pigs and poultry.