Assembly of helper NLR resistosome clusters upon activation of a coiled-coil NLR
Summary
This Nature paper dissects how a coiled-coil NLR (SUMM2), which lacks the typical MADA motif, activates downstream helper NLRs (the ADR1 family) and the EDS1–PAD4 signalling module to drive immune-triggered cell death in Arabidopsis. Key discoveries: many non-MADA CNLs carry an N-myristoylation motif that anchors them to the plasma membrane; SUMM2 is N-myristoylated and this modification is essential for its PM localisation, stability and cell-death activity; on activation SUMM2 promotes assembly of EDS1–PAD4–ADR1 complexes; ADR1-L1 oligomerises into resistosomes that cluster into ring-like assemblies at the inner face of the PM; these organised clusters precede cell death and correlate with Ca2+ influx. Imaging (confocal, TIRF, single-particle tracking), co-IP, FRET-FLIM and biochemical assays underpin the model that non-MADA CNLs recruit helper resistosome clusters rather than forming membrane-penetrating pores themselves.
Key Points
- Many group-II (non-MADA) CNLs have an N-myristoylation motif (MGxxxS/T) that targets them to the plasma membrane.
- SUMM2 is N-myristoylated in planta; mutation of the glycine (G2A) disrupts PM localisation, reduces protein stability and abolishes SUMM2-triggered cell death.
- SUMM2 activation engages the EDS1–PAD4–ADR1 signalling branch (not the EDS1–SAG101–NRG1 branch) to mediate autoimmunity and cell death.
- Activation causes PAD4–EDS1 to dissociate from SUMM2 and associate with ADR1s; ADR1-L1 oligomerises into resistosomes that assemble into discrete, immobile, ring-like clusters at the PM.
- TIR-derived small molecules (TIR enzymatic activity) and Ca2+ signalling contribute: nicotinamide (a TIR inhibitor) blocks cluster formation, Ca2+ influx and cell death; Ca2+ blockers suppress SUMM2 ac-triggered cell death.
- Single-molecule TIRF and tracking show ADR1-L1 transitions from mobile individual foci to organised clusters of 2–6 resistosomes, building progressively before visible cell death.
- Similar resistosome clustering was observed for helper NRCs in Solanum, suggesting clustering may be a general feature of helper NLR activation.
Content summary
The authors combine genetics, biochemistry and high-resolution live-cell imaging to reveal a two-step logic for SUMM2-triggered immunity. In the resting state SUMM2 sequesters EDS1–PAD4 at the PM; upon activation (for example by MEKK1 silencing or expression of an autoactive SUMM2 mutant) SUMM2 remains PM-associated via N-myristoylation but promotes release of EDS1–PAD4. Freed EDS1–PAD4 binds ADR1s, driving ADR1-L1 oligomerisation into resistosomes. These ADR1 resistosomes further cluster into organised, ring-like assemblies embedded in the PM. Cluster formation precedes Ca2+ influx and cell death, and is dependent on EDS1 and PAD4 and on TIR-associated nucleotide signals. The work contrasts SUMM2-type non-MADA CNL behaviour with MADA-containing CNLs (like ZAR1) that form small pore-like resistosomes which penetrate the membrane; here the sensor tethers and nucleates higher-order helper clusters to execute the immune response.
Context and relevance
The paper clarifies how different classes of plant CNLs deploy distinct mechanisms to elicit cell death and defence signalling. Rather than a single universal resistosome mode, some sensors (non-MADA CNLs) act as membrane-tethered organisers that recruit EDS1–PAD4 and helper NLRs to form larger supramolecular assemblies. This refines models of NLR signalling and is important for anyone studying plant innate immunity, NLR engineering for disease resistance, or the cell biology of immune signalosomes.
Author
Punchy: The authors have peeled back a key mechanistic layer of plant immunity — SUMM2 doesn’t punch a hole itself, it calls in the cavalry. If you work on NLR signalling or engineering resistance, the imaging and genetic dissection here are must-see: they show how membrane tethering, helper recruitment and nucleotide signalling knit together to trigger cell death.
Why should I read this?
Short version: if your work touches plant NLRs, immunity or membrane signalling, this paper explains a brand-new activation route that changes how we think helper NLRs execute defence — and they use slick single-molecule and live-cell imaging to prove it. Saves you time: read this and you’ll get the model and the key assays without wading through dozens of separate studies.