Abstract
PVS (potato vetispiradiene synthase) is a key enzyme for synthesis of isoprenoid phytoalexins lubimin and rishitin in potato. Complementary DNAs encoding PVS1 to 4 were isolated. The role of potato phytoalexins in defense response has not been fully understood. We developed transgenic potato plants knocked down PVSs by RNAi. Phytoalexin acumulation was deficient in the transgenic potato tubers after inoculation with Phytophthora infestans. Transgenic tubers showed trailing necrosis like cell death to infection of avirulent P. infestans and high susceptibility to virulent P. infestans. In wild-type leaves, avirulent P. infestans failed to penetrate the epidermal cells and HR cell death was observed in the attacked cells. In contrast, secondary hyphae and HR cell death were observed around mesophyll cells in RNAi leaf-avirulent P. infestans interactions, even though phytoalexin acumulation has not been reported in wild-type leaves. In addtion, RNAi leaves increase disease susceptibility to virulent P. infestans. These results suggest that phytoalexins contribute to disease resistance against P. infestans with other defense-related factors in not only potato tubers but also leaves.
