The Ca(2+)-dependent SOS pathway has emerged as a key mechanism in the homeostasis of Na(+) and K(+) under saline conditions. We recently identified and functionally characterized by complementation studies in yeast and Arabidopsis the gene encoding the calcineurin-interacting protein kinase of the SOS pathway in tomato, SlSOS2.(1) We also show evidences on the biotechnological potential of SlSOS2 conferring salt tolerance to transgenic tomato. The increased salinity tolerance of SlSOS2 overexpressing plants is associated with higher sodium content in stems and leaves. SlSOS2 overexpression upregulates the Na(+)/H(+) exchange at the plasma membrane (SlSOS1) and K(+), Na(+)/H(+) antiport at the endosomal and vacuolar compartments (LeNHX2 and LeNHX4). Therefore, SlSOS2 seems to be involved in tomato salinity tolerance through regulation of Na(+) extrusion from the root, active loading of Na(+) into the xylem and Na(+) and K(+) compartmentalization.