Over-expression of l-gulono-gamma-lactone oxidase (GLOase) gene leads to ascorbate accumulation with enhanced abiotic stress tolerance in tomato

Abstract

Vitamin C (ascorbic acid, AsA) is an essential component for collagen biosynthesis and also for correct functioning of the cardiovascular system in humans. Plants and several animals can synthesize ascorbic acid, whereas humans lack the gene essential for ascorbic acid biosynthesis and must acquire the vitamin from their diet. In the present study, we developed a transgenic tomato plant (Lycopersicon esculentum Mill.) over-expressing the rat l-gulono-gamma-lactone oxidase (GLOase) gene driven by CaMV35S constitutive promoter. The over-expression of GLOase resulted in a 1.5-fold increase in AsA levels in transgenic tomato fruits, which was positively correlated with increased GLOase activity. The Southern and reverse transcriptase polymerase chain reaction results revealed the stable integration of the transgene in the progeny of the engineered plants. The transgenic plants with increased vitamin C content in the fruit showed enhanced tolerance to abiotic stresses induced by methyl viologen, NaCl, and mannitol as compared with wild-type plants. The leaf disc senescence assay showed better tolerance in transgenic plants by retaining higher chlorophyll content compared with wild-type plants. The T-1 plants survived under salt stress (200 mM NaCl) whereas wild-type plants were unable to survive such high salt concentrations. This study suggests that the increased accumulation of AsA could upregulate the antioxidant system which imparts improved tolerance against various abiotic stresses in transgenic tomato plants as compared with wild-type plants.