Ptr1 and ZAR1 immune receptors confer overlapping and distinct bacterial pathogen effector specificities

Abstract

Summary Some nucleotide‐binding and leucine‐rich repeat receptors (NLRs) indirectly detect pathogen effectors by monitoring their host targets. In Arabidopsis thaliana, RIN4 is targeted by multiple sequence‐unrelated effectors and activates immune responses mediated by RPM1 and RPS2. These effectors trigger cell death in Nicotiana benthamiana, but the corresponding NLRs have yet not been identified. To identify N. benthamiana NLRs (NbNLRs) that recognize Arabidopsis RIN4‐targeting effectors, we conducted a rapid reverse genetic screen using an NbNLR VIGS library. We identified that the N. benthamiana homolog of Ptr1 (Pseudomonas tomato race 1) recognizes the Pseudomonas effectors AvrRpt2, AvrRpm1, and AvrB. We demonstrated that recognition of the Xanthomonas effector AvrBsT and the Pseudomonas effector HopZ5 is conferred independently by the N. benthamiana homolog of Ptr1 and ZAR1. Interestingly, the recognition of HopZ5 and AvrBsT is contributed unequally by Ptr1 and ZAR1 in N. benthamiana and Capsicum annuum. In addition, we showed that the RLCK XII family protein JIM2 is required for the NbZAR1‐dependent recognition of AvrBsT and HopZ5. The recognition of sequence‐unrelated effectors by NbPtr1 and NbZAR1 provides an additional example of convergently evolved effector recognition. Identification of key components involved in Ptr1 and ZAR1‐mediated immunity could reveal unique mechanisms of expanded effector recognition.

Helper NLRs Nrc2 and Nrc3 act codependently with Prf/Pto and activate MAPK signaling to induce immunity in tomato

“…The CC‐NLR‐encoding Ptr1 gene, which was identified recently in a wild relative of tomato, S. lycopersicoides , confers resistance to Pst , Xanthomonas spp., and Ralstonia pseudosolanacearum by detecting multiple sequence‐diverse type III effectors, including AvrRpt2 (Ahn, Kim, et al., 2023; Kim et al., 2022, 2023; Mazo‐Molina et al., 2019, 2020; Tsakiri et al., 2023). It is unknown whether any Nrc protein is required for Ptr1‐mediated immunity.…”

NbPTR1confers resistance againstPseudomonas syringae pv. actinidiaein kiwifruit

“…While HopZ5-triggered HR was reduced by m1 expression in the transient assay, ion leakage was only partially reduced (Figure 1e). Ahn et al 27 found that Nb ZAR1 was also involved in the recognition of HopZ5 in N. benthamiana. Therefore, we identified two silencing fragments from our hairpin library, m16 and u38, which correspond to the nucleotide-binding-ARC (NB-ARC) domain or the coiled-coil (CC) domain of Nb ZAR1 , respectively (Figure S2a).…”

“…Several RIN4-related NLR genes have been identified, including At RPS2 , Md Mr5 , Sl Ptr1 , Gm RPG1r , Gm RPG1b , At RPM1 , At ZAR1 , and Nb ZAR1 15,17–19,26,27 . To understand the broader relationships of Ac PTR1 homologues with these NLR proteins involved in recognition of RIN4-associated effectors, the NB-ARC domains of each NLR protein were also included in our phylogenetic analysis (Figure 3a).…”

“…chinensis ‘Hort16A’ plants and did not trigger an HR. Both RPM1 and PTR1 play an important role in HopZ5-triggered immunity in A. thaliana and N. benthamiana , respectively 26,27 . This suggested that transformation of either At RPM1 or Nb PTR1 into kiwifruit might trigger recognition of HopZ5 and be associated with resistance to Psa3.…”

“…MACULICOLA 1) is required for HopZ5-triggered immunity in Arabidopsis , responding to HopZ5’s acetylation of threonine residue T166 of AtRIN4 26 . In N. benthamiana, HopZ5 recognition depends on several NLR genes, PTR1 ( PSEUDOMONAS TOMATO RACE 1 ) and ZAR1 ( HOPZ-ACTIVATED RESISTANCE 1 ) with the assistance of JIM2 ( XOPJ4 IMMUNITY 2 ) for the latter 27 . The evaluation of a set of Psa3 effector knockouts suggests that HopZ5 is not recognised in susceptible A. chinensis 28 .…”