Two linked pairs of Arabidopsis TNL resistance genes independently confer recognition of bacterial effector AvrRps4

Abstract

Plant immunity requires recognition of pathogen effectors by intracellular NB-LRR immune receptors encoded by Resistance (R) genes. Most R proteins recognize a specific effector, but some function in pairs that recognize multiple effectors. Arabidopsis thaliana TIR-NB-LRR proteins RRS1-R and RPS4 together recognize two bacterial effectors, AvrRps4 from Pseudomonas syringae and PopP2 from Ralstonia solanacearum. However, AvrRps4, but not PopP2, is recognized in rrs1/rps4 mutants. We reveal an R gene pair that resembles and is linked to RRS1/RPS4, designated as RRS1B/RPS4B, which confers recognition of AvrRps4 but not PopP2. Like RRS1/RPS4, RRS1B/RPS4B proteins associate and activate defence genes upon AvrRps4 recognition. Inappropriate combinations (RRS1/RPS4B or RRS1B/RPS4) are non-functional and this specificity is not TIR domain dependent. Distinct putative orthologues of both pairs are maintained in the genomes of Arabidopsis thaliana relatives and are likely derived from a common ancestor pair. Our results provide novel insights into paired R gene function and evolution. Plant immunity requires recognition of pathogen effector proteins by specific intracellular immune receptors. Here, Saucet et al. identify an additional pair of Arabidopsis receptors that act together to trigger defence responses upon recognition of the AvrRps4 effector from the bacterial pathogen Pseudomonas syringae.