Deletion of the N-terminal domain of the yeast vacuolar (Na+ ,K+ )/H+ antiporter Vnx1p improves salt tolerance in yeast and transgenic Arabidopsis

Abstract

Cation/proton antiporters play a major role in the control of cytosolic ion concentrations in prokaryotes and eukaryotes organisms. In yeast, we previously demonstrated that Vnx1p is a vacuolar monovalent cation/H⁺ exchanger showing Na⁺ /H⁺ and K⁺ /H⁺ antiporter activity. We have also shown that disruption of VNX1 results in an almost complete abolishment of vacuolar Na⁺ /H⁺ exchange, but yeast cells overexpressing the complete protein do not show improved salinity tolerance. In this study, we have identified an autoinhibitory N-terminal domain and have engineered a constitutively activated version of Vnx1p, by removing this domain. Contrary to the wild type protein, the activated protein has a pronounced effect on yeast salt tolerance and vacuolar pH. Expression of this truncated VNX1 gene also improves Arabidopsis salt tolerance and increases Na⁺ and K⁺ accumulation of salt grown plants thus suggesting a biotechnological potential of activated Vnx1p to improve salt tolerance of crop plants.

Keywords: (Na+,K+)/H+ antiporters; Arabidopsis; ion transport; salt tolerance; vacuoles; yeast.