NRG1-mediated recognition of HopQ1 reveals a link between PAMP and Effector-triggered Immunity.

Members of the HopQ1/XopQ family of effectors are conserved amongst pathogenic bacteria suggesting an important function in virulence. Therefore, the identification of R proteins recognising members of this family is potentially of high value to achieve broad-spectrum resistance in crops. Recent studies demonstrated that HopQ1/XopQ recognition is EDS1-dependant and is mediated by the TIR-NB-LRR protein Roq1. Using our recently described R gene RNAi library, we have investigated the mechanism of HopQ1 recognition and the other components of its signalling network. We show that silencing of the CCR-NB-LRR helper protein N Requirement Gene 1 (NRG1) prevents HopQ1 recognition in N. benthamiana and that NRG1 expression confers recognition of HopQ1 and restricts Pto DC3000 proliferation in the otherwise susceptible host Arabidopsis. Moreover NRG1 expression is briefly but strongly induced at a very early stage of the plant innate response, establishing a strong dependency link between PAMP-triggered immunity (PTI) and effector-triggered immunity (ETI). Overall we demonstrate that in addition to Roq1, HopQ1 recognition in N. benthamiana requires the CCR-NB-LRR protein NRG1 and propose a model based on the dual requirement of a CCR-NB-LRR and a TIR-NB-LRR that could extend beyond HopQ1 detection and possibly be used to recognize other pathogen effectors.