Hemant Ritturaj Kushwaha

Background: Metallothioneins (MT) are low molecular weight, cysteine rich metal binding proteins, found across genera and species, but their function(s) in abiotic stress tolerance are not well documented. Results: We have characterized a rice MT gene, OsMT1e-P, isolated from a subtractive library generated from a stressed salinity tolerant rice genotype, Pokkali. Bioinformatics analysis of the rice genome sequence revealed that this gene belongs to a multigenic family, which consists of 13 genes with 15 protein products. OsMT1e-P is located on chromosome XI, away from the majority of other type I genes that are clustered on chromosome XII. Various members of this MT gene cluster showed a tight co-regulation pattern under several abiotic stresses. Sequence analysis revealed the presence of conserved cysteine residues in OsMT1e-P protein. Salinity stress was found to regulate the transcript abundance of OsMT1e-P in a developmental and organ specific manner. Using transgenic approach, we found a positive correlation between ectopic expression of OsMT1e-P and stress tolerance. Our experiments further suggest ROS scavenging to be the possible mechanism for multiple stress tolerance conferred by OsMT1e-P. Conclusion: We present an overview of MTs, describing their gene structure, genome localization and expression patterns under salinity and development in rice. We have found that ectopic expression of OsMT1e-P enhances tolerance towards multiple abiotic stresses in transgenic tobacco and the resultant plants could survive and set viable seeds under saline conditions. Taken together, the experiments presented here have indicated that ectopic expression of OsMT1e-P protects against oxidative stress primarily through efficient scavenging of reactive oxygen species.

Background: In Arabidopsis thaliana (L.) Heynh and Oryza sativa L., a large number of genes encode proteins of unknown functions, whose characterization still remains one of the major challenges. With an aim to characterize these unknown proteins having defined features (PDFs) in plants, we have chosen to work on proteins having a cystathionine β-synthase (CBS) domain. CBS domain as such has no defined function(s) but plays a regulatory role for many enzymes and thus helps in maintaining the intracellular redox balance. Its function as sensor of cellular energy has also been widely suggested. Results: Our analysis has identified 34 CBS domain containing proteins (CDCPs) in Arabidopsis and 59 in Oryza. In most of these proteins, CBS domain coexists with other functional domain(s), which may indicate towards their probable functions. In order to investigate the role(s) of these CDCPs, we have carried out their detailed analysis in whole genomes of Arabidopsis and Oryza, including their classification, nomenclature, sequence analysis, domain analysis, chromosomal locations, phylogenetic relationships and their expression patterns using public databases (MPSS database and microarray data). We have found that the transcript levels of some members of this family are altered in response to various stresses such as salinity, drought, cold, high temperature, UV, wounding and genotoxic stress, in both root and shoot tissues. This data would be helpful in exploring the so far obscure functions of CBS domain and CBS domain-containing proteins in plant stress responses. Conclusion: We have identified, classified and suggested the nomenclature of CDCPs in Arabidopsis and Oryza. A comprehensive analysis of expression patterns for CDCPs using the already existing transcriptome profiles and MPSS database reveals that a few CDCPs may have an important role in stress response/tolerance and development in plants, which needs to be validated further through functional genomics.