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

Abstract

In certain plant hybrids, autoimmunity is triggered by immune components that interactin 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 HR4 Fei-0 but not the closely related HR4 Col-0 protein directly disrupts intramolecular association of RPP7b Lerik1-3 , which in turn initiates P-loop dependent NLR signaling. In agreement, RPP7b Lerik1-3 forms a higher-order complex only in the presence of HR4 Fei-0 but not HR4 Col-0 . In addition, we find that HR4 Fei-0 on its own can form detergent-resistant oligomers suggestive of amyloid-like aggregates, which in turn can directly kill cells in an RPP7b Lerik1-3 -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.

An rpw8 quadruple mutant of Arabidopsis Col-0 is partially compromised in bacterial and fungal resistance

“…By contrast, loss of all four RPW8 homologs compromised resistance against P. syringae and powdery mildew (Figure 6, Figure 8 and Figure 9). These observations, together with the earlier findings that RPW8 enhances resistance against an oomycete (Hpa) and interacts with RPP7 (Wang et al, 2007;Li et al, 2019), suggest that RPW8 plays an important role in plant immunity but is dispensable for the HR. However, unlike plant MLKLs whose role in cell death is unclear (Mahdi et al, 2019), overexpression of wildtype RPW8 homologs or variants or C-terminal YFP-tagged HR3 results in cell death (Xiao et al, 2003;Wang et al, 2013;Berkey et al, 2017).…”

“…Based on previous characterisation of RPW8 (Xiao et al, 2005;Collier et al, 2011;Barragan et al, 2019;Li et al, 2019), we propose the following two hypotheses that could explain the molecular and biochemical function of RPW8. The first hypothesis posits that RPW8 homologs and the RPW8 domain in RPW8-NLRs participate in activation of immune responses through oligomerization and membrane insertion (pore-forming), thus contributing to HR and pathogen resistance.…”

Evolution of Plant NLRs: From Natural History to Precise Modifications

“…Rapid generation of new recognition specificity can come at a cost: autoimmunity (19,32). Several allelic variants of NLRs have been linked to autoimmunity in Arabidopsis (3,31,77), representing a possible mismatch of NLRs and their guardees. An allelic variant of the A. thaliana NLR RPP7 was recently shown to cause an autoimmune response when combined with incompatible alleles of RPW8 (67).…”

Plant NLRs: The Whistleblowers of Plant Immunity

“…NLR pentamerization, on the other hand, seems to be a more common event. For example, the NLR RPP7 was recently found to self-associate in clusters of five ( Li et al., 2019 ). It may be interesting to discover whether other NLRs can be found to also oligomerize into these larger structures.…”