Ni transporting function of ZIP/Nramp family transporters in Ni hyperaccumulator plant Thlaspi japonicum

摘要

Ni-hyperaccumulator plants accumulate Ni to a level harmful for cell bioactivity, and it is speculated that cells of these plants have some functions of regulating the Ni~(2+) concentration to avoid serious Ni~(2+) damage. To clarify the participationof ZIP and Nramp metal transporters in Ni homeostasis in a Ni hyperaccumulator Thlaspi japonicum, we isolated three ZIP/Nramp homologues from Thlaspi japonicum cDNA and investigated their Ni transporting abilities by expression in yeast. The deduced amino acid sequences of cloned ZIP transporter genes, designed as TjZNT1 and TjZNT2, and those of the Nramp transporter gene TjNramp1, had high homologies with TcZNT1 and TcZNT2 of Thlaspi caemlescens and AtNramp4 of Arabidopsis thaliana, respectively, andwere recognized as putative integral membrane proteins. The yeast transformed with TjZNTl or TjZNT2 had increased Ni tolerance transiently expressing the gene, and slightly decreased the amount of Ni in the cell. In contrast, the expression of TjNrampl caused elevation of Ni sensitivity and Ni concentration. These data suggest that ZIP/Nramp transporters have abilities to transport Ni and function to maintain Ni homeostasis in plants.