Expression analysis of new Metallothionein2-like protein under mercury stress in tomato seedling

Plants including tomato produce several kinds of chelator proteins such as metallothioneins (MTs) for protection against Hg 2+ toxicity. However, the mechanism of protection from Hg 2+ is not perfectly clear. Hg 2+ content subsequently was plateaued from days 1 to 7. Cell death and DNA digestion were not observed in the primary root in the presence of Hg 2+ over the 7 days. The predicted protein sequences of 5 tomato type 2 MT-like (MT2-like) proteins were compared. The coding sequences of accession number Z68185 had no Cys-Cys motif in the N-terminal. However, the Z68185 cDNA genetic recombinant showed high resistance to Hg 2+ in bacteria. In tomato, the expression was observed in the roots, but not in the leaves or stems. mRNA of the MT2-like protein was measured in tomato seedlings exposed to 1 μM Hg 2+ . The expression level did not increase until day 3, but increased expression was observed after day 5. These results suggest that new Metallothionein2-like protein express in root specific and it may trap mercury. Our results indicate that functional identification of an MT2-like protein will be useful for molecular breeding designed to improve plant tolerance to Hg 2+ .