Cysteine (Cys) is the first identified molecule in plant metabolism which includes both sulfur and nitrogen. It can be synthesized in three cellular compartments, containing chloroplast, cytoplasm and mitochondrion. The final step of cysteine biosynthesis is catalyzed by the O-acetylserine(thiol)lyase enzyme (OASTL, E.C. 4.2.99). In the present study, seven members of the OASTL gene family in the sorghum (Sorghum bicolor) genome were identified at a genome-wide scale and comparative bioinformatics analyses were performed between sorghum and Arabidopsis OASTLs. In all OASTL proteins, a pyridoxal-phosphate dependent domain structure (PALP, PF00291) was identified. The gene ontology annotations also revealed that all sorghum OASTL genes have KOG1252 (Cystathionine beta-synthase and related enzyme) and K01738 (cysteine synthase A) activities. In promotor sequences of OASTL genes, diverse cis-acting elements were found, including hormone and light responsiveness, abiotic stress responsiveness, and tissue-specific ones (meristem and endosperm). Sorghum OASTL genes demonstrated medium or high level expressions in anatomical parts and developmental stages based on the digital expression data. Expression of OASTL genes were also analyzed under cadmium (Cd) stress in sorghum by Real Time-quantitative PCR (RT-qPCR). The results exclusively showed that OASTL A1-2 gene was 1.12 fold up-regulated in roots, whereas cysteine synthase 26 was 2.25 fold down-regulated in leaves. The predicted 3D structure of OASTLs indicated some structural diversities as well as variations in the secondary structures.
Keywords: Bioinformatics; Cadmium; Co-expression; Cysteine; Sorghum; Sulfur.