Current status of research on o-acetylserine (thiol) lyase and β-cyanoalanine synthase, two enzymes of plant cysteine biosynthesis- a review

The production of cysteine is the first major significant event in the plant sulfate assimilation process. Cysteine is a precursor of many important biological molecules. Two of the enzymes involved in cysteine biosynthesis are beta-cyanoalanine synthase (CAS) and o-acetylserine (thiol) lyase, members of the Beta-subsituted alanine synthase (Bsas) gene family. There were about forty Bsas genes cloned and characterized from a wide range of plant families in a span of about two decades. Some information on the molecular and biochemical characteristics, as well as subcellular localization of the Bsas genes were recorded. Several reports concurred that the Bsas genes are regulated by external factors such as sulfur and nitrogen availability. More research work toward the elucidation of as many cysteine biosynthesis genes as possible is needed because the biochemical functions of majority of such genes deposited in the databases have not yet been proven. The results will have direct applications in sulfur-related genetic engineering of plants such as breeding for higher protein content.