Elementary Steps in Plant‐Pathogen Recognition Revealed by Enhancing the Stability and Structure of Domains of Plant Innate Immune Receptors

Abstract

Pathogens elicit an immune response in plants through the recognition of the avirulent effectors by multi‐domain intracellular disease resistance receptors. The nature and specificity of plant‐pathogen interactions and the molecular mechanism of eliciting an immune response is being explored using the N protein from Nicotianaglutinosa. The N protein is an archetype of the nucleotide binding (NB), leucine rich repeat (LRR) family of innate immune receptors (NLRs), and the interaction with its avirulent effector, the helicase domain (HEL) of the replicase protein of tobacco mosaic virus (TMV) triggers a classic hypersensitive cell death response in plants. An initial step in activating cell death pathways upon pathogen recognition is a structure change that enables NLR assembly through their N‐terminal Toll‐Interlukin1 Receptor‐like (TIR) domains. Stabilized domains with increased tendency to self‐associate have been constructed by focused mutagenesis guided by computational modeling of a 3.0 Å crystal structure of the N‐TIR domain. The energetics of TIR dimerization is being correlated with the severity of the hypersensitive response by measuring salicylic acid using LC‐MS to examine the hypothesis that receptor assembly is correlated with NLR signaling. Yeast surface display is being used to probe the manner whereby host NLRs recognize pathogenic determinants, and reveals that the interaction of N with its pathogen effector, the HEL domain of TMV, is mediated via its LRR domain. Binding analyses show that a stabilized LRR domain binds HEL about 250‐fold more strongly than a non‐virulent homologue that does not display a hypersensitive response. Variants of the full‐length N protein are being rebuilt from the individually stabilized TIR and LRR domains optimized for functional analyses to enable biochemical and structural investigations of plant NLR receptors.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.