Bacteria establish an aqueous living space in plants crucial for virulence

Nature. 2016 Nov 24;539(7630):524-529. doi: 10.1038/nature20166.


High humidity has a strong influence on the development of numerous diseases affecting the above-ground parts of plants (the phyllosphere) in crop fields and natural ecosystems, but the molecular basis of this humidity effect is not understood. Previous studies have emphasized immune suppression as a key step in bacterial pathogenesis. Here we show that humidity-dependent, pathogen-driven establishment of an aqueous intercellular space (apoplast) is another important step in bacterial infection of the phyllosphere. Bacterial effectors, such as Pseudomonas syringae HopM1, induce establishment of the aqueous apoplast and are sufficient to transform non-pathogenic P. syringae strains into virulent pathogens in immunodeficient Arabidopsis thaliana under high humidity. Arabidopsis quadruple mutants simultaneously defective in a host target (AtMIN7) of HopM1 and in pattern-triggered immunity could not only be used to reconstitute the basic features of bacterial infection, but also exhibited humidity-dependent dyshomeostasis of the endophytic commensal bacterial community in the phyllosphere. These results highlight a new conceptual framework for understanding diverse phyllosphere-bacterial interactions.

MeSH terms

  • Arabidopsis / immunology
  • Arabidopsis / metabolism
  • Arabidopsis / microbiology*
  • Arabidopsis Proteins / metabolism
  • Bacterial Proteins / metabolism
  • Guanine Nucleotide Exchange Factors
  • Homeostasis
  • Host-Pathogen Interactions*
  • Humidity*
  • Immune Tolerance
  • Plant Diseases / immunology
  • Plant Diseases / microbiology*
  • Plant Immunity
  • Plant Leaves / immunology
  • Plant Leaves / microbiology*
  • Pseudomonas syringae / genetics
  • Pseudomonas syringae / immunology
  • Pseudomonas syringae / metabolism
  • Pseudomonas syringae / pathogenicity*
  • Symbiosis
  • Virulence / immunology
  • Water / metabolism*


  • Arabidopsis Proteins
  • At3g43300 protein, Arabidopsis
  • Bacterial Proteins
  • Guanine Nucleotide Exchange Factors
  • Water