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Title:   Author  item
                                            McClean, Aliitem
                                            Kluepfel, Daniel
  Submitted to: Phytopathology
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 10/3/2008
                                    Publication  Date: 2/1/2009
                                    Citation: Mcclean, A.E., Kluepfel, D.A. 2009. GENETIC LOCI INVOLVED IN RUBRIFACINE PRODUCTION IN THE WALNUT PATHOGEN BRENNARIA RUBRIFACIENS. Phytopathology. 99:145-151.Interpretive Summary: The bacterium Brenneria rubrifaciens causes deep bark canker of walnut.  When grown in vitro B. rubrifaciens produces a red pigment called rubrifacine.  Analysis of DNA flanking the Tn5 insertion site in 21 pigment minus (pig -) mutants identified 3 regions required for rubrifacine production. The first region was homologous to non-ribosomal peptide synthetases (NRPS), the second was homologous to autoinducer synthetase genes (expI homologs) and the third region was homologous to the slyA gene of Candidatus blochmania and Escherichia coli.  Pigment production was not necessary for elicitation of the hypersensitive response (HR) in tobacco or virulence in tissue-cultured walnut plants.  The expI interrupted mutants exhibited reduced virulence on walnut and were HR negative on tobacco.  Pigment production was restored in Br-212 when grown in the presence of wildtype B. rubrifaceins, E. coli carrying the cloned expI-like gene or introduction of the cloned wildtype copy of the expI-like gene into Br-212. Two Brenneria species, B. nigrifluens and B.  salicis also restored pigment production in Br-212.  These results demonstrate that rubrifacine production and virulence in B. rubrifaciens are under the control of a quorum sensing system and are sensitive to signal molecules from other Brenneria species.
                                Technical Abstract: The bacterium Brenneria rubrifaciens causes deep bark canker of walnut.  When grown in vitro B. rubrifaciens produces a red pigment called rubrifacine.  Analysis of DNA flanking the Tn5 insertion site in 21 pigment minus (pig -) mutants identified 3 regions required for rubrifacine production. The first region was homologous to non-ribosomal peptide synthetases (NRPS), the second was homologous to autoinducer synthetase genes (expI homologs) and the third region was homologous to the slyA gene of Candidatus blochmania and Escherichia coli.  Pigment production was not necessary for elicitation of the hypersensitive response (HR) in tobacco or virulence in tissue-cultured walnut plants.  The expI interrupted mutants exhibited reduced virulence on walnut and were HR negative on tobacco.  Pigment production was restored in Br-212 when grown in the presence of wildtype B. rubrifaceins, E. coli carrying the cloned expI-like gene or introduction of the cloned wildtype copy of the expI-like gene into Br-212. Two Brenneria species, B. nigrifluens and B.  salicis also restored pigment production in Br-212.  These results demonstrate that rubrifacine production and virulence in B. rubrifaciens are under the control of a quorum sensing system and are sensitive to signal molecules from other Brenneria species.


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