Taking the lead: NLR immune receptor N‐terminal domains execute plant immune responses

Abstract

SummaryNucleotide‐binding domain and leucine‐rich repeat (NLR) proteins are important intracellular immune receptors that activate robust plant immune responses upon detecting pathogens. Canonical NLRs consist of a conserved tripartite architecture that includes a central regulatory nucleotide‐binding domain, C‐terminal leucine‐rich repeats, and variable N‐terminal domains that directly participate in immune execution. In flowering plants, the vast majority of NLR N‐terminal domains belong to the coiled‐coil, Resistance to Powdery Mildew 8, or Toll/interleukin‐1 receptor subfamilies, with recent structural and biochemical studies providing detailed mechanistic insights into their functions. In this insight review, we focus on the immune‐related biochemistries of known plant NLR N‐terminal domains and discuss the evolutionary diversity of atypical NLR domains in nonflowering plants. We further contrast these observations against the known diversity of NLR‐related receptors from microbes to metazoans across the tree of life.

Conifers Concentrate Large Numbers of NLR Immune Receptor Genes on One Chromosome

“… Guillet-Claude et al 2004 ), should also be considered (e.g. Chia and Carella 2023 ). In particular, the more accurate functional characterization of transcripts through long transcriptome sequencing (e.g.…”

“…The products of NLR genes occur intracellularly and can bind directly to specific pathogenic effectors (pathogen-encoded proteins) or detect modifications of plant proteins induced by such effectors, thus activating a cascade of defense mechanisms upon perception ( Ngou et al 2022 ). NLRs provide a typical example of an evolutionary arms race in which pathogenic effectors evolve to evade detection by host NLRs, which, in turn, evolve to recognize the new variants ( Chen et al 2023 ; Chia and Carella 2023 ). NLRs are therefore diverse and abundant in many plant species with several hundred different NLR genes found in a range of land plant lineages ( Barragan and Weigel 2021 ).…”

Conifers concentrate large numbers of NLR immune receptor genes on one chromosome

“…The genomic sequences identified here may prompt further work to determine which of these are expressed and under what circumstances. Studies of functional divergence among sequences and of evolutionary rates, aiming at identifying footprints of natural selection (e.g., Guillet-Claude et al 2004) should also be considered (e.g., Chia and Carella 2023).…”

The N-terminal domains of NLR immune receptors exhibit structural and functional similarities across divergent plant lineages

“…NLR NTDs are viewed as the “executioner” or “signaling” domain encoding the biochemical activities that lead to immunity. Indeed, ectopic expression of NTDs in planta, either alone or translationally fused to fluorescent proteins like yellow fluorescent protein (YFP), is often sufficient to promote domain self-association and activate plant immune responses ( Bernoux et al 2011 ; Bentham et al 2018 ; Chia and Carella 2023 ). Typical outputs downstream of NLR NTD activity include defensive hormone accumulation/signaling, transcriptional reprogramming, reactive oxygen species (ROS) accumulation, and in many cases a localized form of programmed cell death known as the hypersensitive response (HR) ( Lolle et al 2020 ; Dalio et al 2021 ).…”