gamma-Aminobutyric acid (GABA) accumulates in many plant species in response to environmental stress. However, the physiological function of GABA or its metabolic pathway (GABA shunt) in plants remains largely unclear. Here, the genes, including glutamate decarboxylases (SlGADs), GABAtransaminases (SlGABA-Ts) and succinic semialdehyde dehydrogenase (SlSSADH), controlling three steps of the metabolic pathway of GABA, were studied through virus-induced gene silencing approach in tomato. Silencing of SlGADs (GABA biosynthetic genes) and SlGABA-Ts (GABA catabolic genes) led to increased accumulation of reactive oxygen species (ROS) as well as salt sensitivity under 200mm NaCl treatment. Targeted quantitative analysis of metabolites revealed that GABA decreased and increased in the SlGADs- and SlGABA-Ts-silenced plants, respectively, whereas succinate (the final product of GABA metabolism) decreased in both silenced plants. Contrarily, SlSSADH-silenced plants, also defective in GABA degradation process, showed dwarf phenotype, curled leaves and enhanced accumulation of ROS in normal conditions, suggesting the involvement of a bypath for succinic semialdehyde catabolism to -hydroxybutyrate as reported previously in Arabidopsis, were less sensitive to salt stress. These results suggest that GABA shunt is involved in salt tolerance of tomato, probably by affecting the homeostasis of metabolites such as succinate and -hydroxybutyrate and subsequent ROS accumulation under salt stress. -Aminobutyric acid (GABA) accumulates in many plant species in response to environmental stress, but the physiological function of GABA or its metabolic pathway (GABA shunt) in plants remains largely unclear. In the present study, based on loss-of-function studies, our findings revealed the functional involvement of GABA shunt in the salt tolerance of tomato and the putative roles for GABA-related metabolites (such as succinate and -hydroxybutyrate) in these processes. These results open exciting perspectives for further investigations of GABA shunt and associated metabolic pathways to the stress adaptation of plants, pointing to these pathways as potential targets for engineering of plant stress tolerance. To our knowledge, this work represents one of the most thorough studies demonstrating the roles of GABA metabolic pathway in defense against environmental stress.