Some plant species carry scores or even hundreds of different NLR immune receptor genes, with extensive allelic diversity and presence/absence polymorphism (Barragan & Weigel, 2021).
R genes usually encode NLR immune receptors (Meyers et al, 1999). Plant breeders have long exploited this genetic variation to elevate crop varietal resistance by introgression of multiple disease Resistance ( R) genes from wild relatives. Natural plant populations carry extensive genetic variation in immune receptor repertoires (Ngou et al, 2022b). Activation of defense requires detection, both by cell surface receptors that usually detect relatively conserved pathogen-derived molecules such as flagellin or chitin (Lee et al, 2021), and by intracellular nucleotide-binding, leucine-rich repeat (NLR) receptors which detect effectors that often function for the pathogen to attenuate plant defenses (Jones et al, 2016). Plants have powerful defense mechanisms, but to be effective, these must be rapidly activated at sites of attempted pathogen ingress. Mechanistic understanding of NRC resistosome formation will underpin engineering crops with durable disease resistance.
NRC2 resistosome can be activated by Rpi-amr3 upon detection of AVRamr3 homologs from other Phytophthora species. ATP-binding motifs of both Rpi-amr3 and NRC2 are required for NRC2 resistosome formation, but not for the interaction of Rpi-amr3 with its cognate effector. The activated NRC2 oligomer becomes enriched in membrane fractions. In contrast, recognition of P. infestans effector AVRamr1 by another sensor NLR Rpi-amr1 induces formation of only the NRC2 resistosome. We show here that Rpi-amr3, a sensor NLR from Solanum americanum, detects AVRamr3 from the potato late blight pathogen, Phytophthora infestans, and activates oligomerization of helper NLRs NRC2 and NRC4 into high-molecular-weight resistosomes. Many Solanaceae NLRs require NRC (NLR-Required for Cell death) class of helper NLRs. Most “sensor” NLRs that detect effectors require the activity of “helper” NLRs, but how helper NLRs support sensor NLR function is poorly understood. Plants have evolved robust innate immunity that depends in part on intracellular Nucleotide-binding, Leucine rich-Repeat (NLR) immune receptors that activate defense responses upon detection of pathogen-derived effectors.
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