Enhanced cadmium accumulation and tolerance in transgenic tobacco overexpressing rice metal tolerance protein gene OsMTP1 is promising for phytoremediation

• The full length coding DNA sequence of OsMTP1 belonging to plant CDF/MTP family was isolated from indica rice cultivar IR64.
• The OsMTP1 gene expression was found to be significantly upregulated in seeds and leaves but downregulated in roots of rice plant upon cadmium (Cd) stress.
• Heterologous expression of OsMTP1 in tobacco significantly reduced the Cd stress-induced phytotoxicity, such as growth inhibition, lipid peroxidation and cell death.
• Transgenic tobacco plants exhibited significantly higher growth pattern, enhanced vacuolar thiol content and hyperaccumulated Cd compared to untransformed control under Cd exposure.
• Transgenic tobacco plants expressing OsMTP1 could be useful for future phytoremediation applications to clean up Cd contaminated soil.

One of the most grievous heavy metal pollutants in the environment is cadmium (Cd), which is not only responsible for the crop yield loss owing to its phytotoxicity, but also for the human health hazards as the toxic elements usually accumulate in the consumable parts of crop plants. In the present study, we aimed to isolate and functionally characterize the OsMTP1 gene from indica rice (Oryza sativa L. cv. IR64) to study its potential application for efficient phytoremediation of Cd. The 1257 bp coding DNA sequence (CDS) of OsMTP1 encodes a ∼46 kDa protein belonging to the cation diffusion facilitator (CDF) or metal tolerance/transport protein (MTP) family. The OsMTP1 transcript in rice plant was found to respond during external Cd stress. Heterologous expression of OsMTP1 in tobacco resulted in the reduction of Cd stress-induced phytotoxic effects, including growth inhibition, lipid peroxidation, and cell death. Compared to untransformed control, the transgenic tobacco plants showed enhanced vacuolar thiol content, indicating vacuolar localization of the sequestered Cd. The transgenic tobacco plants exhibited significantly higher biomass growth (2.2–2.8-folds) and hyperaccumulation of Cd (1.96–2.22-folds) compared to untransformed control under Cd exposure. The transgenic plants also showed moderate tolerance and accumulation of arsenic (As) upon exogenous As stress, signifying broad substrate specificity of OsMTP1. Together, findings of our research suggest that the transgenic tobacco plants overexpressing OsMTP1 with its hyperaccumulating activity and increased growth rate could be useful for future phytoremediation applications to clean up the Cd-contaminated soil.