A wheat resistosome defines common principles of immune receptor channels

Abstract

Plant intracellular nucleotide-binding leucine-rich repeat (NLRs) receptors detect pathogen effectors to trigger immune responses. Indirect recognition of a pathogen effector by the dicotyledonous Arabidopsis thaliana coiled-coil (CC) domain containing NLR (CNL) ZAR1 induces the formation of a large hetero-oligomeric protein complex, termed the ZAR1 resistosome, which functions as a calcium channel required for ZAR1-mediated immunity (1-3). Whether the resistosome and channel activities are conserved among plant CNLs remains unknown. We report here a cryogenic electron microscopy (cryo-EM) structure of the wheat CNL Sr35 in complex with the effector AvrSr35 of the wheat stem rust pathogen at 3.0 [A] resolution. Direct effector binding to the leucine-rich repeats (LRRs) of Sr35 results in the formation of a pentameric Sr35-AvrSr35 complex, which we designate the Sr35 resistosome. Wheat Sr35 and Arabidopsis ZAR1 resistosomes bear striking structural similarity, including a previously unnoticed arginine cluster in the LRR domain that co-occurs and forms intramolecular interactions with the EDVID motif in the CC domain. Electrophysiological measurements show that the Sr35 resistosome exhibits non-selective cation channel activity. These structural insights allowed us to generate novel variants of closely related wheat and barley orphan NLRs that recognize AvrSr35. Our data support the evolutionary conservation of CNL resistosomes in plants and demonstrate proof of principle for structure-based engineering of NLRs for crop improvement.