BRASSINOSTEROID-SIGNALING KINASE1 Phosphorylates MAPKKK5 to Regulate Immunity in Arabidopsis

Plant Physiol. 2018 Apr;176(4):2991-3002. doi: 10.1104/pp.17.01757. Epub 2018 Feb 12.

Abstract

Arabidopsis (Arabidopsis thaliana) immune receptor FLAGELLIN SENSING2 (FLS2) rapidly forms a complex to activate pathogen-associated molecular pattern-triggered immunity (PTI) upon perception of the bacterial protein flagellin. The receptor-like cytoplasmic kinase BRASSINOSTEROID-SIGNALINGKINASE1 (BSK1) interacts with FLS2 and is critical for the activation of PTI. However, it is unknown how BSK1 transduces signals to activate downstream immune responses. We identified MEK Kinase5 (MAPKKK5) as a potential substrate of BSK1 by whole-genome phosphorylation analysis. In addition, we demonstrated that BSK1 interacts with and phosphorylates MAPKKK5. In the bsk1-1 mutant, the Ser-289 residue of MAPKKK5 was not phosphorylated as it was in the wild type. Similar to the bsk1 mutant, the mapkkk5 mutant displayed enhanced susceptibility to virulent and avirulent strains of the bacterial pathogen Pseudomonas syringae pv tomato DC3000, and to the fungal powdery mildew pathogen Golovinomyces cichoracearum Phosphorylation of the Ser-289 residue is not involved in MAPKKK5-triggered cell death but is critical for MAPKKK5-mediated resistance to both bacterial and fungal pathogens. Furthermore, MAPKKK5 interacts with multiple MAPK kinases, including MKK1, MKK2, MKK4, MKK5, and MKK6. Overall, these results indicate that BSK1 regulates plant immunity by phosphorylating MAPKKK5 and suggest a direct regulatory mode of signaling from the immune complex to the MAPK cascade.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / genetics*
  • Arabidopsis / metabolism
  • Arabidopsis / microbiology
  • Arabidopsis Proteins / genetics*
  • Arabidopsis Proteins / metabolism
  • Ascomycota / physiology
  • Disease Resistance / genetics
  • Gene Expression Regulation, Plant
  • Host-Pathogen Interactions
  • MAP Kinase Kinase Kinase 5 / genetics*
  • MAP Kinase Kinase Kinase 5 / metabolism
  • Mitogen-Activated Protein Kinases / metabolism
  • Mutation*
  • Phosphorylation
  • Plant Diseases / genetics
  • Plant Diseases / microbiology
  • Plant Immunity / genetics*
  • Protein Binding
  • Protein Serine-Threonine Kinases / genetics*
  • Protein Serine-Threonine Kinases / metabolism
  • Pseudomonas syringae / physiology
  • Serine / genetics
  • Serine / metabolism

Substances

  • Arabidopsis Proteins
  • Serine
  • Protein Serine-Threonine Kinases
  • brassinosteroid-signaling kinase1, Arabidopsis
  • Mitogen-Activated Protein Kinases
  • MAP Kinase Kinase Kinase 5