Structural basis of NLR activation and innate immune signalling in plants

Mohammad Kawsar Manik,Xiahao Hu,Bryan Y. J. Lim,Hayden Burdett,Natsumi Maruta,Sneha Desa,Bostjan Kobe

doi:10.1007/s00251-021-01242-5

Abstract

Animals and plants have NLRs (nucleotide-binding leucine-rich repeat receptors) that recognize the presence of pathogens and initiate innate immune responses. In plants, there are three types of NLRs distinguished by their N-terminal domain: the CC (coiled-coil) domain NLRs, the TIR (Toll/interleukin-1 receptor) domain NLRs and the RPW8 (resistance to powdery mildew 8)-like coiled-coil domain NLRs. CC-NLRs (CNLs) and TIR-NLRs (TNLs) generally act as sensors of effectors secreted by pathogens, while RPW8-NLRs (RNLs) signal downstream of many sensor NLRs and are called helper NLRs. Recent studies have revealed three dimensional structures of a CNL (ZAR1) including its inactive, intermediate and active oligomeric state, as well as TNLs (RPP1 and ROQ1) in their active oligomeric states. Furthermore, accumulating evidence suggests that members of the family of lipase-like EDS1 (enhanced disease susceptibility 1) proteins, which are uniquely found in seed plants, play a key role in providing a link between sensor NLRs and helper NLRs during innate immune responses. Here, we summarize the implications of the plant NLR structures that provide insights into distinct mechanisms of action by the different sensor NLRs and discuss plant NLR-mediated innate immune signalling pathways involving the EDS1 family proteins and RNLs.

Highlights

Plant pathogenic microbes pose a major threat to global crop production
N AD+ cleavage activity by plant Toll interleukin-1 receptor (TIR) domains leads to the formation of nicotinamide and plant-specific variant cyclic ADPR (v-cADPR) (Wan et al 2019), which potentially acts as a signal to initiate EDS1-helper nucleotide-binding leucinerich repeat receptors (NLRs)-mediated immune pathways to trigger cell death
There are still important questions to be answered about the nature of NLR activation and the effector-triggered immunity (ETI) pathways

Summary

Introduction

Plant pathogenic microbes pose a major threat to global crop production. To induce efficient defence responses and confer disease resistance, plants rely on two distinct types of innate immune receptors. N AD+ cleavage activity by plant TIR domains leads to the formation of nicotinamide and plant-specific variant cyclic ADPR (v-cADPR) (Wan et al 2019), which potentially acts as a signal to initiate EDS1-helper NLR-mediated immune pathways to trigger cell death.

Results

Conclusion