Over-Expression of Tomato GDP-Mannose Pyrophosphorylase (GMPase) in Potato Increases Ascorbate Content and Delays Plant Senescence

GDP-D-mannose pyrophosphorylase (GMPase) catalyses the synthesis of GDP-D-mannose and represents the first committed step in the synthesis of ascorbate. In the present study, the GMPase gene of tomato was introduced into potato by Agrobacterium-mediated transformation. Two transgenic lines with higher GMPase expression were selected using qPCR and protein blot analyses. The results showed that the content of L-ascorbic acid (AsA) and the ratio of AsA/DHA (dehydroascorbate) significantly increased in both leaves and tubers of transgenic potato plants. Both pigment content and photosynthetic rate were much higher in transgenic plants than in wild-type plants. Transgenic plants showed a distinguishable change in phenotype from the wild-type plants. Furthermore, transgenic plants showed delayed senescence.