Overexpression of the tomato K + /H + antiporter LeNHX2 confers salt tolerance by improving potassium compartmentalization

• Here, the function of the tomato (Solanum lycopersicon) K +/H+ antiporter LeNHX2 was studied using 35S-driven gene overexpression of a histagged LeNHX2 protein in Arabidopsis thaliana and LeNHX2 gene silencing in tomato. • Transgenic A. thaliana plants expressed the histagged LeNHX2 both in shoots and in roots, as assayed by western blotting. Transitory expression of a green fluorescent protein (GFP) tagged protein showed that the antiporter is present in small vesicles. Internal membrane vesicles from transgenic plants displayed enhanced K+/H+ exchange activity, confirming the K+/H+ antiporter function of this enzyme. Transgenic A. thaliana plants overexpressing the histagged tomato antiporter LeNHX2 exhibited inhibited growth in the absence of K+ in the growth medium, but were more tolerant to high concentrations of Na + than untransformed controls. When grown in the presence of NaCl, transgenic plants contained lower concentrations of intracellular Na +, but more K+, as compared with untransformed controls. • Silencing of LeNHX2 in S. lycopersicon plants produced significant inhibition of plant growth and fruit and seed production as well as increased sensitivity to NaCl. • The data indicate that regulation of K+ homeostasis by LeNHX2 is essential for normal plant growth and development, and plays an important role in the response to salt stress by improving K + accumulation.