Heterologous expression of the metallothionein PpMT2 gene from Physcomitrella patens confers enhanced tolerance to heavy metal stress on transgenic Arabidopsis plants

Metallothioneins (MTs) play essential roles in plant resistance to heavy metal stress, as well as in the scavenging of reactive oxygen species. A number of metallothionein genes in angiosperm have been identified. However, their functions in Physcomitrella patens are still largely unknown. In this work, the function of PpMT2, a metallothionein encoding gene from Physcomitrella patens, was investigated. Sequence alignment and phylogenetic analyses demonstrated that PpMT2 encoded a metallothionein with conserved sequences as other MTs from Arabidopsis, rice, soybean, black nightshade, sedum and poke weed. RT-PCR analyses revealed that PpMT2 was strongly induced by CuSO4 and CdCl2 in Physcomitrella patens. Heterologous expression of PpMT2 led to improved tolerance to high concentrations of CuSO4 and CdCl2 in both Y2HGold yeast cells and transgenic Arabidopsis plants. These findings suggest that PpMT2 is involved in heavy metal stress responses in Physcomitrella patens, and could be used as a potential candidate gene for the genetic engineering of plants with improved resistance to heavy metal stress.