An RXLR Effector Secreted by Phytophthora parasitica is a Virulence Factor and Triggers Cell Death in Various Plants
Guiyan Huang, Zhirou Liu, Biao Gu, Hong Zhao, Jinbu Jia, Guangjin Fan, Yuling Meng, Yu Du, Weixing Shan.
Molecular Plant Pathology
Abstract: RXLR effectors encoded by Phytophthora species play a central role in pathogen-plant interactions. Understanding the biological functions of RXLR effectors are conducive to illuminating pathogenic mechanisms and developing disease-control strategies. However, the virulence function of Phytophthora parasitica RXLR effectors is poorly understood. Here, we describe the identification of a P. parasitica RXLR effector gene, PPTG00121 (PpE4), which is highly transcribed during the early stages of infection and conserved among various Phytophthora species. Live-cell imaging of P. parasitica transformants expressing a full-length PpE4 (E4FL)-mCherry protein indicated that PpE4 is secreted and accumulates around haustoria during plant infection. Silencing of PpE4 in P. parasitica resulted in significantly reduced virulence on Nicotiana benthamiana. Transient expression of PpE4 in N. benthamiana in turn restored pathogenicity of the PpE4-silenced lines. Furthermore, expression of PpE4 in both N. benthamiana and Arabidopsis thaliana consistently enhanced plant susceptibility to P. parasitica. These results indicate that PpE4 contributes to pathogen infection. Finally, heterologous expression experiments showed that PpE4 triggers nonspecific cell death in a variety of plants including tobacco, tomato, potato, and A. thaliana. Virus-induced gene silencing assays revealed that PpE4-induced cell death is HSP90-, NPK-, and SGT1-dependent, suggesting that PpE4 is recognized by the plant immune system. In conclusion, PpE4 is an important virulence RXLR effector of P. parasitica that is conserved across Phytophthora species and recognized by a wide range of host plants.