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.
Keywords: LeNHX4 antiporter; Proline; Protein; Salinity tolerance; Solanum lycopersicum; Soluble sugars.