Ectopic expression of FaGalUR leads to ascorbate accumulation with enhanced oxidative stress, cold, and salt tolerance in tomato

l-Ascorbic acid (vitamin C, AsA), is an essential component for collagen biosynthesis and the major antioxidant in human, mainly obtained from the diet. Strawberry as fruit with higher AsA concentration processes a distinct AsA biosynthesis pathway from tomato (Solanum lycopersicum) which dominants in d-mannose/l-galactose pathway. Firstly, the activity of d-galacturonic acid reductase (GalUR; EC = 1.1.1.19) parallel to AsA accumulation in crude extract of tomato leaves and fruits was detected. Subsequently, transgenic tomato lines overexpressing strawberry FaGalUR gene resulted in twofold and 1.6-fold increase in AsA level in tomato fruit and leaf, respectively, which correlated positively with FaGalUR transcriptional abundance and GalUR activity. Furthermore, FaGalUR-overexpressing plants showed enhanced tolerance to abiotic stresses induced by oxidization (methyl viologen), salt (NaCl) and cold as compared to the wild-type plants. Taken together, the present findings suggest that tomato might share the alternative d-galacturonate pathway for ascorbate biosynthesis, and abiotic stress tolerance as well as AsA accumulation in tomato can be enhanced by regulating strawberry GalUR gene.