Overexpression of LeNHX4 improved yield, fruit quality and salt tolerance in tomato plants (Solanum lycopersicum L.).

The function of the tomato K+, Na+/H+ antiporter LeNHX4 has been analyzed using 35S-driven gene construct for overexpressing a histagged LeNHX4 protein in Solanum lycopersicum L. Compared to wild-type plants, the expression of LeNHX4 was enhanced in most of plants transformed with a gene construct for LeNHX4 overexpression although some plants showed a decreased LeNHX4 expression. Overexpression of LeNHX4 was associated to an increased fruit size while silencing of this gene was related to a decreased fruit size. We have investigated the effect of LeNHX4 overexpression on fruit production and quality and we have also evaluated salt tolerance in two different overexpression lines by measuring proline, protein and glucose concentrations in tomato leaves grown either under control (0 mM NaCl) or saline (125 mM NaCl) conditions. Plants overexpressing LeNHX4 showed a higher amount of fruits than WT plants and accumulated higher contents of sugars and cations (Na+ and K+). The application of 125 mM NaCl, affected negatively fruit production and quality of WT plants. However the transgenic lines overexpressing LeNXH4 increased fruit quality and yield. In relation to salt tolerance, overexpression lines showed higher levels of leaf proline, glucose and proteins under NaCl treatment. The overexpression of LeNHX4 in tomato plants, improved salinity tolerance and increased fruit yield and quality under both normal and salinity stress conditions.

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.