The Na+/H+ exchanger SOS1 controls extrusion and distribution of Na+ in tomato plants under salinity conditions

Maintaining a high K+/Na+ ratio in the cell cytosol, along with the transport processes implicated in the xylem and phloem loading/unloading of Na+ in plants (long-distance transport) are key aspects in plant salt tolerance. The Ca2+-dependent SOS pathway regulating Na+ and K+ homeostasis and long-distance Na+ transport has been reported in Arabidopsis. However, Arabidopsis might not be the best model to analyze the involvement of the SOS pathway in long-distance Na+ transport due to the very short stem of these plants which do not allow a precise dissection of the relative content of Na+ in stem versus leaf. This separation would be critical to assess the role of SOS1 in xylem loading/unloading, Na+ export by roots, retention in stems and the differential distribution/accumulation in old leaves. Towards this goal, tomato might represent a superior model due to its anatomical structure and agricultural significance. We recently demonstrated the key role played by the plasma membrane Na+/H+ antiporter SlSOS1 in salt tolerance in tomato by maintaining ion homeostasis under salinity stress and in the partitioning of Na+ in plant organs.