Elevated Expression of Vacuolar Nickel Transporter Gene Is Associated With Reduced Root-to-Shoot Nickel Translocation in .

A number of metal hyperaccumulator plants, including nickel (Ni) hyperaccumulators, have been identified in the genus . The ability to accumulate Ni in shoots varies widely among species and ecotypes in this genus; however, little is known about the molecular mechanisms underlying this intra- and inter-specific variation. Here, in hydroponic culture, we compared Ni accumulation patterns between , which originated in Ni-enriched serpentine soils in Mt. Yubari (Hokkaido, Japan), and ecotype Ganges, which originated in zinc/lead-mine soils in Southern France. Both species showed extremely high Ni tolerance compared with that of the non-accumulator . But, following treatment with 200 μM Ni, showed leaf chlorosis, whereas did not show any stress symptoms. Shoot Ni concentration was higher in than in ; this difference was due to higher efficiency of root-to-shoot Ni translocation in than . It is known that the vacuole Ni transporter IREG2 suppresses Ni translocation from roots to shoots by sequestering Ni in the root vacuoles. The expression level of the gene in the roots of was 10-fold that in the roots of . Moreover, the copy number of per genome was higher in than in , suggesting that expression is elevated by gene multiplication in . The heterologous expression of of and in yeast and confirmed that both genes encode functional vacuole Ni transporters. Taking these results together, we hypothesize that the elevation of expression by gene multiplication causes the lower root-to-shoot Ni translocation in .