Oligomerization of the NLR immune receptor RPP7 triggered by the atypical resistance protein RPW8/HR as a ligand

In certain plant hybrids, autoimmunity is triggered by immune components that interact in the absence of a pathogen trigger. Often, NLR immune receptors are involved, with a particularly interesting case in Arabidopsis thaliana involving variants of the NLR RPP7 as well as variants of RPW8/HR proteins, which are homologs of animal MLKL and fungal HELL domain proteins. We demonstrate that HR4Fei-0 but not the closely related HR4Col-0 protein directly disrupts intramolecular association of RPP7bLerik1-3, which in turn initiates P-loop dependent NLR signaling. In agreement, RPP7bLerik1-3 forms a higher-order complex only in the presence of HR4Fei-0 but not HR4Col-0. In addition, we find that HR4Fei-0 on its own can form detergent-resistant oligomers suggestive of amyloid-like aggregates, which in turn can directly kill cells in an RPP7bLerik1-3-independent manner. Our work provides in vivo biochemical evidence for a plant resistosome complex and the mechanisms by which RPW8/HR proteins trigger cell death.