An RXLR effector secreted by Phytophthora parasitica is a virulence factor and triggers cell death in various plants

Abstract

RXLR effectors encoded by Phytophthora species play a central role in pathogen–plant interactions. An understanding of the biological functions of RXLR effectors is conducive to the illumination of the pathogenic mechanisms and the development of 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. 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 the pathogenicity of the PpE4-silenced lines. Furthermore, the 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 non-specific 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 dependent on HSP90, NPK and SGT1, suggesting that PpE4 is recognized by the plant immune system. In conclusion, PpE4 is an important virulence RXLR effector of P. parasitica and recognized by a wide range of host plants.