Characterization of genes encoding metal tolerance proteins isolated from Nicotiana glauca and Nicotiana tabacum

We have isolated a metal tolerance protein (MTP) gene, NgMTP1, from Nicotiana glauca (a potential phytoremediator plant) and two MTP genes, NtMTP1a and NtMTP1b, from Nicotiana tabacum. These three genes shared approximately 95% homology at the amino acid level. Heterologous expression of any of these three genes complemented Zn and Co tolerance in yeast mutants to a similar extent. In yeast, these proteins were shown to be located to vacuole membrane. These results suggest that the three MTPs operate by sequestering Zn and Co into vacuoles, thereby reducing the toxicity of these metals.