LAUSR

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.