Plant receptor-like protein activation by a microbial glycoside hydrolase

Nature. 2022 Oct;610(7931):335-342. doi: 10.1038/s41586-022-05214-x. Epub 2022 Sep 21.

Abstract

Plants rely on cell-surface-localized pattern recognition receptors to detect pathogen- or host-derived danger signals and trigger an immune response1-6. Receptor-like proteins (RLPs) with a leucine-rich repeat (LRR) ectodomain constitute a subgroup of pattern recognition receptors and play a critical role in plant immunity1-3. Mechanisms underlying ligand recognition and activation of LRR-RLPs remain elusive. Here we report a crystal structure of the LRR-RLP RXEG1 from Nicotiana benthamiana that recognizes XEG1 xyloglucanase from the pathogen Phytophthora sojae. The structure reveals that specific XEG1 recognition is predominantly mediated by an amino-terminal and a carboxy-terminal loop-out region (RXEG1(ID)) of RXEG1. The two loops bind to the active-site groove of XEG1, inhibiting its enzymatic activity and suppressing Phytophthora infection of N. benthamiana. Binding of XEG1 promotes association of RXEG1(LRR) with the LRR-type co-receptor BAK1 through RXEG1(ID) and the last four conserved LRRs to trigger RXEG1-mediated immune responses. Comparison of the structures of apo-RXEG1(LRR), XEG1-RXEG1(LRR) and XEG1-BAK1-RXEG1(LRR) shows that binding of XEG1 induces conformational changes in the N-terminal region of RXEG1(ID) and enhances structural flexibility of the BAK1-associating regions of RXEG1(LRR). These changes allow fold switching of RXEG1(ID) for recruitment of BAK1(LRR). Our data reveal a conserved mechanism of ligand-induced heterodimerization of an LRR-RLP with BAK1 and suggest a dual function for the LRR-RLP in plant immunity.

MeSH terms

  • Amino Acid Motifs
  • Binding Sites
  • Crystallography, X-Ray
  • Glycoside Hydrolases* / metabolism
  • Leucine / metabolism
  • Ligands
  • Phytophthora* / enzymology
  • Phytophthora* / immunology
  • Phytophthora* / physiology
  • Plant Immunity*
  • Plant Proteins* / chemistry
  • Plant Proteins* / immunology
  • Plant Proteins* / metabolism
  • Protein Multimerization
  • Receptors, Pattern Recognition* / chemistry
  • Receptors, Pattern Recognition* / immunology
  • Receptors, Pattern Recognition* / metabolism
  • Tobacco / chemistry
  • Tobacco / metabolism

Substances

  • Ligands
  • Plant Proteins
  • Receptors, Pattern Recognition
  • Glycoside Hydrolases
  • Leucine