摘要Plant intracellular nucleotide binding leucine-rich repeat (NLR) immune receptors play critical roles in pathogen surveillance.Most plant NLRs characterized so far were found to use a single domain/sensor to recognize pathogen effectors.Here we report that the Sw-5b NLR immune receptor uses two distinct domains to detect the viral movement protein NSm encoded by tospovirus.In addition to its leucine-rich repeat (LRR) domain that has been previously reported,the N-terminal Solanaceae domain (SD) of Sw5b also interacts with NSm and a conserved 21-amino-acid region of NSm (NSm21).The specific interaction between Sw-5b SD and NSm is required for releasing the inhibitory effect of coiled-coil domain on the NB-ARC-LRR region.Furthermore,we found that the binding of NSm affects the nucleotide binding activity of the NB-ARC-LRR in vitro,while Sw-5b NB-ARC-LRR is activated only when NSm and NSm21 levels are high.Interestingly,Sw-5b SD could significantly enhance the ability of the NB-ARC-LRR to detect low levels of NSm effector and facilitate its activation and induction of defense response.An Sw-5b SD mutant that is disrupted in NSm recognition failed to enhance the ability of the NB-ARC-LRR to sense low levels of NSm and NSm21.Taken together,our results suggest that Sw-5b SD functions as an extra sensor and the NB-ARC-LRR as an activator,and that Sw-5b NLR adopts a two-step recognition mechanism to enhance viral effector perception.