Abstact

Pathogens counteract central nodes of NLR immune receptor networks to suppress immunity. However, the mechanisms by which pathogens hijack helper NLR pathways are poorly understood. We show that an effector from the late blight pathogen Phytophthora infestans interacts with the host protein NbTOL9a and a helper NLR to suppress immunity. We solved the crystal structure of the RXLR-LWY effector AVRcap1b in complex with the ENTH domain of NbTOL9a. The structure revealed that, unlike other RXLR-LWY effectors, AVRcap1b has a previously unidentified L-shaped fold that defines a distinct structural family of effectors in the genus Phytophthora. We defined the AVRcap1b/NbTOL9a binding interface and designed effector mutants that do not bind NbTOL9a, impairing immune suppression. This suggests that ENTH binding is required for full virulence activity. Last, we show that AVRcap1b associates specifically with activated NbNRC2 independently of NbTOL9a binding. We propose a model in which the effector interconnects NbNRC2 with the NbTOL9a pathway. Our results illustrate a previously uncharacterized pathogen mechanism to hijack NLR pathways and suppress immunity.