Abstract
The beta-substituted alanine (Ala) synthase (Bsas) family in the large superfamily of pyridoxal 5'-phosphate-dependent enzymes comprises cysteine (Cys) synthase (CSase) [O-acetyl-serine (thiol) lyase] and beta-cyano-Ala synthase (CASase) in plants. Nine genomic sequences encode putative Bsas proteins in Arabidopsis thaliana. The physiological roles of these Bsas isoforms in vivo were investigated by the characterization of T-DNA insertion mutants. Analyses of gene expression, activities of CSase and CASase, and levels of Cys and glutathione in the bsas mutants indicated that cytosolic Bsas1;1, plastidic Bsas2;1, and mitochondrial Bsas2;2 play major roles in Cys biosynthesis. Cytosolic Bsas1;1 has the most dominant contribution both in leaf and root, and mitochondrial Bsas2;2 plays a significant role in root. Mitochondrial Bsas3;1 is a genuine CASase. Nontargeted metabolome analyses of knockout mutants were carried out by a combination of gas chromatography time-of-flight mass spectrometry and capillary electrophoresis time-of-flight mass spectrometry. The level of gamma-glutamyl-beta-cyano-Ala decreased in the mutant bsas3;1, indicating the crucial role of Bsas3;1 in beta-cyano-Ala metabolism in vivo.
Highlights
The b-substituted alanine (Ala) synthase (Bsas) family in the large superfamily of pyridoxal 5#-phosphate-dependent enzymes comprises cysteine (Cys) synthase (CSase) [O-acetyl-serine lyase] and b-cyano-Ala synthase (CASase) in plants
Bsas1;1, Bsas2;1, and Bsas2;2, which are localized in the cytosol, plastids, and mitochondria, respectively, of Arabidopsis cells, are considered the predominant Cys synthase (CSase) according to kinetic analysis (Hell et al, 1994, 1999; Hesse and Hofgen, 1998; Wirtz et al, 2004)
Transcripts of the other Bsas genes (Bsas4;1, Bsas4;2, Bsas4;3, and Bsas5;1) could be detected, but at an overall lower expression level. These results for expression levels and tissue specificities were in good agreement with the microarray analysis (Genevestigator; https://www.genevestigator. ethz.ch; Fig. 1B) and the number of ESTs in The Arabidopsis Information Resource (TAIR; http://www. arabidopsis.org; Noji et al, 2006; Fig. 1C)
Summary
The b-substituted alanine (Ala) synthase (Bsas) family in the large superfamily of pyridoxal 5#-phosphate-dependent enzymes comprises cysteine (Cys) synthase (CSase) [O-acetyl-serine (thiol) lyase] and b-cyano-Ala synthase (CASase) in plants. These biochemical characterizations and subcellular localization studies were relatively well conducted, the actual roles of Bsas genes in vivo are not necessarily clear. Questions such as whether each Bsas isoform is redundant or has a specific function in vivo and to what extent each Bsas isoform contributes to the synthesis of Cys and b-cyano-Ala remain unresolved. This article reports the analysis of T-DNA-inserted knockout mutants of Arabidopsis for
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
