The Salt Sensitivity Induced by Disruption of Cell Wall-Associated Kinase 1 (SlWAK1) Tomato Gene Is Linked to Altered Osmotic and Metabolic Homeostasis

Tomato cell wall-associated kinase 1 (SlWAK1) has only been studied in biotic stress response and hence its function in abiotic stress remains unknown. In a screening under salinity of an insertional mutant collection of tomato (Solanum lycopersicumL.), a mutant exhibiting lower degree of leaf chlorosis than wild type (WT) together with reduced leaf Na(+)accumulation was selected. Genetic analysis of the mutation revealed that a single T-DNA insertion in theSlWAK1gene was responsible of the mutant phenotype.Slwak1null mutant reduced its shoot growth compared with WT, despite its improved Na(+)homeostasis.SlWAK1disruption affected osmotic homeostasis, as leaf water content was lower in mutant than in WT under salt stress. In addition,Slwak1altered the source-sink balance under salinity, by increasing sucrose content in roots. Finally, a significant fruit yield reduction was found inSlwak1vs. WT under long-term salt stress, mainly due to lower fruit weight. Our results show that disruption ofSlWAK1induces a higher sucrose transport from source leaf to sink root, negatively affecting fruit, the main sink at adult stage.