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Death switch: how resistosomes activate immunity

Hiroaki Adachi; Sophien Kamoun; Abbas Maqbool

Pathogen perception triggers a monomeric NLR plant immune receptor to form a pentameric wheel-like complex termed a resistosome, with the N-terminal ahelices forming a funnel-shaped structure that may perturb plasma membrane integrity to cause hypersensitive cell death.

Nucleotide-binding leucine-rich repeat (NLR) proteins are intracellular receptors that detect pathogen molecules and activate a robust immune response that includes the hypersensitive response (HR) cell death in plants. Although plant NLRs are known to oilgomerize through their N-terminal domains, such as the coiled coil (CC) domain, the molecular mechanisms that underpin plant NLR activation and the subsequent execution of HR cell death have remained largely unknown. In two recent paradigm-shifting Science papers, Wang et al. have advanced our understanding of both the structural and biochemical bases of NLR activation in plants, creating a new conceptual framework. They reconstituted both the inactive and active complexes of the CC-NLR protein HOPZ-ACTIVATED RESISTANCE1 (ZAR1) with its partner receptor-like cytoplasmic kinases (RLCKs) and used cryo-electron microscopy to show that activated ZAR1 forms a resistosome—a wheel-like pentamer that can switch conformation to expose a funnel-shaped structure formed by the very N-terminal ahelices (a1) of the CC domains. They propose a provocative model in which the five exposeda1 helices of the ZAR1 resistosome form a funnel-like structurethat triggers HR cell death by translocating into the plasma membrane and perturbing membrane integrity similar to pore-forming toxins.

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