Quorum-sensing system affects gall development incited by Pantoea agglomerans pv. gypsophilae

Laura Chalupowicz, Shulamit Manulis-Sasson, Maxim Itkin, Ayelet Sacher, Guido Sessa, Isaac Barash

Research output: Contribution to journalArticlepeer-review

Abstract

The quorum-sensing (QS) regulatory system of the gall-forming Pantoea agglomerans pv. gypsophilae was identified. Mass spectral analysis, together with signal-specific biosensors, demonstrated that P. agglomerans pv. gypsophilae produced N-butanoyl-L-homoserine lactone (C4-HSL) as a major and N-hexanoyl-L-homoserine lactone (C6-HSL) as a minor QS signal. Homologs of luxI and luxR regulatory genes, pagI and pagR, were characterized in strain P. agglomerans pv. gypsophilae Pag824-1 and shown to be convergently transcribed and separated by 14 bp. The deduced PagI (23.8 kDa) and PagR (26.9 kDa) show high similarity with SmaI (41% identity) and SmaR (43% identity), respectively, of Serratia sp. American Type Culture Collection 39006. PagR possesses characteristic autoinducer binding and a helix-turn-helix DNA-binding domain. Gall formation by P. agglomerans pv. gypsophilae depends on a plasmid-borne hrp/hrc gene cluster, type III effectors, and phytohormones. Disruption of pagI, pagR, or both genes simultaneously in Pag824-1 reduced gall size in gypsophila cuttings by 50 to 55% when plants were inoculated with 106 CFU/ml. Higher reductions in gall size (70 to 90%) were achieved by overexpression of pagI or addition of exogenous C4-HSL. Expression of the hrp/hrc regulatory gene hrpL and the type III effector pthG in the pagI mutant, as measured with quantitative reverse-transcriptase polymerase chain reaction, was reduced by 5.8 and 6.6, respectively, compared with the wild type, suggesting an effect of the QS system on the Hrp regulon.

Original languageEnglish
Pages (from-to)1094-1105
Number of pages12
JournalMolecular Plant-Microbe Interactions
Volume21
Issue number8
DOIs
StatePublished - Aug 2008

Keywords

  • Pathogenicity island
  • pPATH
  • pPATH

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