Abstract
BackgroundMetallothioneins (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.ResultsWe 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.ConclusionWe 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.
Highlights
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
Increase in the transcript was observed in both Wild type (WT) and transgenic lines when subjected to salinity (200 mM NaCl, Figure 3E, F). These results show that a transcript signal corresponding to the size of OsMT1e-P transcript was detected in WT tobacco plants under stress conditions, when rice OsMT1e-P gene was used as probe
Ectopic expression of OsMT1e-P in tobacco provides multiple stress tolerance in subsequent generations Since we found that transgenic tobacco seedlings (T1) outperform the WT plants in the leaf disc assays under salinity stress (Additional file 3: Figure S3), we decided to extend the analysis to T2 generation and various abiotic stresses such as dehydrations (PEG), cold, heavy metals (ZnSO4 and CuSO4) and high temperature
Summary
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. Plant MTs identified so far contain two cysteine-rich domains and a large spacer region (30–50 a.a. residues, devoid of cysteine) [5,6]. Based on the distribution of cysteine residues, number of aromatic amino acids as well as length of the spacer region, plant MTs are further classified into four types, type 1 through 4 [1,6,7]. The antioxidant function of MTs is attributed to the presence of a large number of cysteine residues, which besides metal binding are capable of ROS scavenging [6]. In rice, several type 1 and type 2 MTs have been found to play a direct role in antioxidation [16]
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