Improving Ni2+ Tolerance of Arabidopsis by Overexpressing Bacterial rcnA Gene Encoding a Membrane-Bound Exporter of Ni2+

The prerequisite for breeding a plant to be used in phytoremediation is its high tolerance to grow normally in soil contaminated by certain heavy metals. As mechanisms of plant uptake and transport of nickel (Ni) are not fully understood, it is of significance to utilize exogenous genes for improving plant Ni tolerance. In this study, <i>rcnA</i> from <i>Escherichia coli</i> encoding an exporter of Ni and cobalt was overexpressed constitutively in <i>Arabidopsis thaliana</i>, and the performance of transgenic plants was assayed under Ni stress. The subcellular localization of rcnA in plant cells was found to be the plasma membrane. Constitutive overexpression of <i>rcnA</i> in Arabidopsis rendered better growth of either seedlings on agar medium containing 85, 100, and 120 μM NiCl₂ or adult plants in a nutrient solution with 5 mM NiCl₂ added. Compared to the wildtype, <i>rcnA</i>-OE transgenic plants under Ni stress accumulated lower levels of reactive oxygen species (i.e., superoxide and hydrogen peroxide) in leaves and exhibited less oxidative damage in shoots, as demonstrated by less electrolyte leakage and the lower malondialdehyde content. Notably, <i>rcnA</i>-OE transgenic plants retained a higher content of Ni in roots and had a lower content of Ni in shoots. Therefore, our findings indicated that the bacterial <i>rcnA</i> gene may be utilized to improve plant Ni tolerance through genetic transformation.