Cloning and characterization of a type 1 metallothionein gene from the copper-tolerant plant Elsholtzia haichowensis

EhMT1, a type 1 metallothionein (MT) gene, was cloned from Elsholtzia haichowensis, a Cu-tolerant plant. Typical of plant type 1 MTs, EhMT1 encodes a putative peptide of 74 amino acid residues containing cysteine-rich domains. Sequence comparisons with various databases revealed strong similarities at the nucleotide and amino acid levels between EhMT1 and the type 1 MT of Mimulus guttatus. EhMT1 transcription was greater in the roots than in the leaves, and was markedly increased by treatments with Cu, H2O2, and heat shock. EhMT1-GUS was localized to the cytoplasm of onion epidermal cells. Escherichia coli cells expressing pET-30a-EhMT1 were more tolerant to Cu and accumulated more Cu than control cells. Our results show that EhMT1 is involved in Cu tolerance and accumulation in E. haichowensis.