Regulation of AHL production and its contribution to epiphytic fitness in Pseudomonas syringae

Mol Plant Microbe Interact. 2004 May;17(5):521-31. doi: 10.1094/MPMI.2004.17.5.521.


Pseudomonas syringae forms large cell aggregates that are more stress tolerant than solitary cells during epiphytic growth on plants. The differential survival of aggregates on leaves suggests that epiphytic fitness traits may be controlled in a density-dependent manner via cell-cell signaling. We investigated this hypothesis in P. syringae B728a. Synthesis of N-acyl-homoserine lactone (AHL), 3-oxo-hexanoyl homoserine lactone, and the expression of the gene encoding AHL synthase ahlI were maximal at high cell concentrations. The expression of the AHL regulator ahlR, in contrast, was similar at all cell concentrations. A screen of Tn5 mutants revealed that P. syringae B728a requires a novel transcriptional activator for AHL production. This regulator, which belongs to the TetR family, was also required for epiphytic fitness and has been designated AefR (for AHL and epiphytic fitness regulator). The expression of ahlI was greatly reduced in both aefR- and gacA- mutants and was completely restored in either mutant after addition of exogenous AHL. In contrast, the expression of aefR was not reduced in either gacS- or gacA- mutants. Thus, AefR appears to positively regulate AHL production independently of the regulators GacS/GacA and also controls traits in P. syringae B728a that are required for epiphytic colonization.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 4-Butyrolactone / analogs & derivatives*
  • 4-Butyrolactone / biosynthesis*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Base Sequence
  • Gene Expression Regulation, Bacterial
  • Ligases / genetics
  • Ligases / metabolism
  • Molecular Sequence Data
  • Mutation
  • Plant Diseases / microbiology
  • Pseudomonas syringae / genetics
  • Pseudomonas syringae / metabolism*
  • Pseudomonas syringae / pathogenicity
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism
  • Signal Transduction / genetics
  • Signal Transduction / physiology
  • Trans-Activators / genetics
  • Trans-Activators / metabolism
  • Transcription Factors / genetics
  • Transcription Factors / metabolism


  • Bacterial Proteins
  • LuxI protein, Bacteria
  • Repressor Proteins
  • Trans-Activators
  • Transcription Factors
  • LuxR autoinducer binding proteins
  • homoserine lactone
  • N-(3-oxohexanoyl)-3-aminodihydro-2(3H)-furanone
  • Ligases
  • N-acylhomoserine lactone synthase
  • 4-Butyrolactone

Associated data

  • GENBANK/AJ566342
  • GENBANK/AJ566343
  • GENBANK/AJ567455