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.