The NLR immune receptor Roq1 recognizes the Pseudomonas syringae HopAG1 effector via its Nudix domain

Plant nucleotide-binding leucine-rich repeat receptors (NLRs) sense directly or indirectly effectors - proteins employed by pathogens during infection. While indirect recognition can be initiated by unrelated effectors targeting the same cellular component, direct recognition is restricted by conformational constraints of the pathogen protein and corresponding receptor. Recognition of XopQ (Roq1) receptor confers resistance to bacteria expressing members of the highly conserved effector family comprising XopQ/HopQ1/RipB. The structure of the activated Roq1 was solved previously, revealing that LRR and C-JID domains of Roq1 are involved in XopQ binding. In this study, we found that Roq1 detects HopAG1, a member of a structurally different effector family. Presence of HopAG1 in Pseudomonas syringae reduced bacterial growth and symptoms development in wild-type but not in roq1 Nicotiana benthamiana plants. Moreover, HopAG1 co-immunoprecipitated with Roq1 indicating that both proteins associate. Based on deletion and structural analyses, we postulate that this interaction occurs via the Nudix domain of HopAG1 that binds to a similar receptor interface like XopQ. Nudix fold is predicted in multiple pathogen effectors suggesting that Roq1 may recognize effector families other than XopQ and HopAG1. Accordingly, it is also conceivable that other TNLs may detect a broader range of effector families than supposed.