Immunomodulation by the Pseudomonas syringae HopZ type III effector family in Arabidopsis

PLoS One. 2014 Dec 29;9(12):e116152. doi: 10.1371/journal.pone.0116152. eCollection 2014.


Pseudomonas syringae employs a type III secretion system to inject 20-30 different type III effector (T3SE) proteins into plant host cells. A major role of T3SEs is to suppress plant immune responses and promote bacterial infection. The YopJ/HopZ acetyltransferases are a superfamily of T3SEs found in both plant and animal pathogenic bacteria. In P. syringae, this superfamily includes the evolutionarily diverse HopZ1, HopZ2 and HopZ3 alleles. To investigate the roles of the HopZ family in immunomodulation, we generated dexamethasone-inducible T3SE transgenic lines of Arabidopsis for HopZ family members and characterized them for immune suppression phenotypes. We show that all of the HopZ family members can actively suppress various facets of Arabidopsis immunity in a catalytic residue-dependent manner. HopZ family members can differentially suppress the activation of mitogen-activated protein (MAP) kinase cascades or the production of reactive oxygen species, whereas all members can promote the growth of non-virulent P. syringae. Localization studies show that four of the HopZ family members containing predicted myristoylation sites are localized to the vicinity of the plasma membrane while HopZ3 which lacks the myristoylation site is at least partially nuclear localized, suggesting diversification of immunosuppressive mechanisms. Overall, we demonstrate that despite significant evolutionary diversification, all HopZ family members can suppress immunity in Arabidopsis.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / immunology*
  • Arabidopsis / microbiology*
  • Bacterial Proteins / metabolism*
  • Bacterial Secretion Systems*
  • Biocatalysis
  • Cell Membrane / metabolism
  • Cell Nucleus / metabolism
  • Cysteine / metabolism
  • Disease Resistance / immunology
  • Enzyme Activation
  • Immunomodulation*
  • Mitogen-Activated Protein Kinases / metabolism
  • Phosphorylation
  • Plant Diseases / microbiology
  • Plant Immunity
  • Plant Leaves / microbiology
  • Plants, Genetically Modified
  • Pseudomonas syringae / immunology*
  • Reactive Oxygen Species / metabolism


  • Bacterial Proteins
  • Bacterial Secretion Systems
  • Reactive Oxygen Species
  • Mitogen-Activated Protein Kinases
  • Cysteine

Grants and funding

This work was supported by Natural Sciences and Engineering Research Council of Canada awards to DSG and DD; a Canada Research Chair in Plant-Microbe Systems Biology (DD) or Comparative Genomics (DSG); the Centre for the Analysis of Genome Evolution and Function (DD and DSG); United States Department of Agriculture Agricultural Research Service 5335-21000-040-00D (JDL). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.