Copper-induced hydrogen peroxide upregulation of a metallothionein gene, OsMT2c, from Oryza sativa L. confers copper tolerance in Arabidopsis thaliana

Metallothioneins (MTs) are low-molecular-weight, cysteine-rich metal-binding proteins found in numerous genera and species, but their functions in abiotic stress tolerance remain unclear. Here, a MT gene from Oryza sativa, OsMT2c, was isolated and characterized, encoding a type 2 MT, and observed expression in the roots, leaf sheathes, and leaves, but only weak expression in seeds. OsMT2c was upregulated by copper (Cu) and hydrogen peroxide (H2O2) treatments. Excessive Cu elicited a rapid and sustained production and release of H2O2 in rice, and exogenous H2O2 scavengers N,N'-dimethylthiourea (DMTU) and ascorbic acid (Asc) decreased H2O2 production and OsMT2c expression. Furthermore, the expression of OsMT2c increased in the osapx2 mutant in which the H2O2 levels were higher than in wild-type (WT) plants. These results showed that Cu increased MT2c expression through the production and accumulation of Cu-induced H2O2 in O. sativa. In addition, the transgenic OsMT2c-overexpressing Arabidopsis displayed improved tolerance to Cu stress and exhibited increased reactive oxygen species (ROS) scavenging ability compared to WT and empty-vector (Ev) seedlings.