The metal-binding domain of wheat heavy metal ATPase 2 (TaHMA2) is involved in zinc/cadmium tolerance and translocation in Arabidopsis

Abstract

Cysteine in the N-terminal metal-binding domain (N-MBD) of TaHMA2 participates in Zn²⁺/Cd²⁺ binding and translocation in Arabidopsis. Wheat heavy metal ATPase 2 (TaHMA2) can transport Zn²⁺ and Cd²⁺ across membranes. A previous study showed that cysteine (Cys) and glutamate residues in the N-terminal metal-binding domain (N-MBD) were necessary for metal-binding and translocation of TaHMA2 in yeast. However, the function of TaHMA2 in plants was not fully revealed. In this study, we investigated the roles of the CCxxE and CPC motifs in the N-MBD and the N/C-terminal regions of TaHMA2 in Zn²⁺/Cd²⁺ translocation in root and shoot of Arabidopsis. Compared with the wild type, overexpression of TaHMA2 and the TaHMA2 derivative (glutamic substituted for alanine from CCxxE) in Arabidopsis increased root length, fresh weight and enhanced Zn²⁺/Cd²⁺ root-to-shoot translocation. The plants with a truncated N/C-terminal of TaHMA2 were impaired in Zn²⁺/Cd²⁺ tolerance and translocation, while mutagenesis of Cys in the N-MBD reduced the tolerance and transport activity of TaHMA2, suggesting the involvement of Cys in Zn²⁺/Cd²⁺ binding and translocation in Arabidopsis. This study therefore provides a theoretical possibility for the application of TaHMA2 in transgenic breeding to regulate metal element balance in crop plants.

Keywords: Arabidopsis; Heavy metal; Heavy metal ATPase; Metal-binding domain; Triticum aestivum.