Overexpression of the metallothionein gene PaMT3-1 from Phytolacca americana enhances plant tolerance to cadmium

Metallothionein (MT) is a cysteine-rich, low-molecular-weight protein that can bind to cadmium ions and reduce their toxicity to plants. In this study, we cloned the PaMT3-1 gene encoding an unstable protein of 63 amino acids from the cadmium hyperaccumulator Phytolacca americana. The gene was inserted into a plant expression vector and introduced into tobacco plants. The cadmium content of the transgenic plants was measured after treatment with 100 mM CdCl for 7 days. Transgenic and wild-type roots had similar cadmium contents, whereas the cadmium content of transgenic leaves was 66.28–78.70% of the wild type. The transport coefficient of cadmium in transgenic plants was decreased by 23.31–35.52% relative to the wild type. According to various physiological indexes, including malondialdehyde content, relative electrolyte leakage, root activity, and soluble sugar content, the transgenic plants performed better than the wild type. The PaMT3-1 gene can significantly improve plant resistance to cadmium and has potential as an important gene resource in phytoremediation. Our findings could also contribute to an understanding of complex processes and mechanisms involved in phytoremediation.