Diversity in cadmium accumulation and resistance associated with various metallothionein genes (type III) in Phytolacca americana L

Metallothioneins (MTs) are known for their heavy metal deoxidation during phytoremediation. To estimate their roles in the cadmium (Cd) hyperaccumulator Phytolacca americana L., three MT genes, PaMT3-1, PaMT3-2 and PaMT3-3, belonging to the MT3 subfamily were cloned. They separately encoded 63, 65 and 65 amino acids, containing12, 10 and 11 cysteines (Cys), respectively. Each gene was individually transformed and expressed in Escherichia coli cells. A Cd-resistance assay showed that the recombinant strains had enhanced survival rates, especially those containing PaMT3-1 and PaMT3-3. Additionally, the recombinant strains were high Cd accumulators, with the recombinant PaMT3-1's maximum accumulation being 2.16 times that of the empty vector strains. The numbers of cysteines and the structures of MT proteins were associated with the Cd enrichment and resistance capabilities. PaMT3-1 could be an effective gene resource in future plant Cd remediation-related breeding programs.