P-096 - TIR-NB-LRR locus confers recognition of the Pseudomonas syringae type III effector AvrRps4 in Solanum americanum

Phytopathogens deliver effectors into host plants to manipulate host metabolism and immunity. To counteract the pathogen strategy, plants have developed NLRs that recognize effectors and trigger immune responses, often leading to hypersensitive response (HR). Some NLRs detect effectors through integrated decoy domains mimicking effector targets. Arabidopsis TIR-NLR RRS1 carries a WRKY domain, which belongs to the plant transcription factor family. Another TIR-NLR, RPS4, cooperates with RRS1 to recognize AvrRps4 from Pseudomonas syringae, PopP2 from Ralstonia solanacearum, and XopJ6 from Xanthomonas campestris, which interact with WRKY of RRS1. We found that Solanum americanum recognizes AvrRps4 despite lacking RRS1 or RPS4 homologs. To investigate how S. americanum recognizes AvrRps4, we conducted HR assays in S. americanum using AvrRps4 mutants previously characterized in Arabidopsis. Interestingly, AvrRps4 amino acid residues critical for binding to WRKY of RRS1 were essential for recognition in S. americanum. Furthermore, AvrRps4-triggered HR was abolished in S. americanum eds1 mutants. To identify the NLR responsible, we performed bulk segregant analysis on F₂ populations from a cross between responsive and non-responsive accessions. This revealed a single dominant locus predicted to contain 11 TIR-NLRs, none of which are integrated with WRKY. We propose that a TIR-NLR(s) in S. americanum, non-orthologous to RRS1 and RPS4, recognizes AvrRps4.