Pathogen recognition by nucleotide-binding (NB), leucine-rich repeat (LRR) receptors (NLRs) plays roles in plant resistance. Campestris effector AvrAC uridylylates the Arabidopsis PBL2 kinase, and the latter (PBL2UMP) acts as a ligand to trigger the NLR ZAR1 precomplexed with the RKS1 pseudokinase. Here we report the cryo–electron microscopy structures of ZAR1-RKS1 and ZAR1-RKS1-PBL2UMP within an inactive and intermediate country, respectively. The ZAR1LRR domainname, in comparison with animal NLRLRR domain names, is differently placed to sequester ZAR1 in an inactive state. Recognition of PBL2UMP is only through RKS1, which interacts with ZAR1LRR. PBL2UMP binding stabilizes the RKS1 activation segment, which sterically blocks ZAR1 adenosine diphosphate (ADP) binding. This engenders a NB domain that is more flexible without fluctuations in another ZAR1 domain names. Our analysis provides a template for understanding plant NLRs.