Overexpression of LeNHX2 and SlSOS2 increases salt tolerance and fruit production in double transgenic tomato plants.

Transgenic tomato plants (Solanum lycopersicum L. cv. MicroTom) overexpressing both the K+,Na+/H+ antiporter LeNHX2 and the regulatory kinase SlSOS2 were produced by crossing transgenic homozygous lines overexpressing LeNHX2 and SlSOS2. LeNHX2 expression was enhanced in plants overexpressing LeNHX2 but surprisingly even more in plants overexpressing SlSOS2 with and without LeNHX2. All transgenic plants showed better NaCl tolerance than wild type controls and plants overexpressing both LeNHX2 and SlSOS2 grew better under saline conditions than plants overexpressing only one of these genes. Yield related parameters indicated that single and above all double transgenic plants performed significantly better than wild type controls. All transgenic plants produced fruits with a higher K+ content than wild-type plants and plants overexpressing SlSOS2 accumulated more Na+ in fruits than the rest of the plants when grown with NaCl. Roots, stems and leaves of transgenic plants overexpressing LeNHX2 showed a higher K+ content than wild type and single transgenic plants overexpressing SlSOS2. Na+ content in stems and leaves of NaCl treated plants was higher in SlSOS2 overexpressing plants than in wild type and LeNHX2 single transgenic plants. All transgenic lines showed a higher leaf relative water content and a higher plant water content and water use efficiency than wild type controls when both were grown in the presence of NaCl. Results in this work indicate that the joint overexpression of LeNHX2 and SlSOS2 improves growth and water status under NaCl stress, affects K+ and Na+ homeostasis and enhances fruit yield of tomato plants.