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 CC _R -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 CC _R -NB-LRR protein NRG1 and propose a model based on the dual requirement of a CC _R -NB-LRR and a TIR-NB-LRR that could extend beyond HopQ1 detection and possibly be used to recognize other pathogen effectors.