# Molecular mechanisms of plant NLR activation and signalling

## TL;DR

This review explains how plant NLR receptors detect pathogen proteins and activate immune responses, and how this knowledge can be used to improve plant disease resistance.

## Contribution

The paper provides an updated review of recent structural and functional insights into plant NLR activation and signaling mechanisms.

## Key findings

- NLRs form resistosomes upon effector recognition, initiating immune signaling.
- Some NLRs require helper or paired NLRs to execute immune responses.
- Recent studies have clarified how downstream proteins are recruited for signaling.

## Abstract

Plants rely on NLRs (nucleotide‐binding leucine‐rich repeat receptors) to recognise effector proteins secreted by pathogens into plant cells and to deliver disease resistance. Plant NLRs are broadly characterised by their N‐terminal domains, which include the TIR (Toll/interleukin‐1 receptor) and the CC (coiled‐coil) domains. Effector recognition triggers NLR oligomerisation into complexes termed resistosomes, which initiate immune signalling. Some NLRs function as singletons that detect pathogens and activate immune responses, while there are NLRs that only recognise effectors and thereby require helper NLRs or genetically linked ‘paired’ NLRs to execute immune signalling. Recent studies have enhanced our understanding of the molecular mechanisms of different classes of NLRs, as well as how downstream proteins are recruited to signal upon effector recognition. In this review, we discuss the current knowledge of the NLR activation mechanisms, based on findings from recent structural and functional studies. We also highlight the remaining unknowns in the field and discuss current and potential future applications for enhancing plant immunity by engineering plant NLRs.

Plant NLRs (nucleotide‐binding leucine‐rich repeat receptors) are essential for recognition of pathogen secreted effectors and activation of effector‐triggered immunity. This review focuses on our current understanding of the NLR activation and signalling mechanisms, based on recent structural and functional studies. It also highlights remaining knowledge gaps in the field, and applications for improving disease resistance by NLR engineering approaches.