title: The phytoalexin-inducible multidrug efflux pump AcrAB contributes to virulence in the fire blight pathogen, Erwinia amylovora.
abstract: The enterobacterium Erwinia amylovora causes fire blight on members of the family Rosaceae, with economic importance on apple and pear. During pathogenesis, the bacterium is exposed to a variety of plant-borne antimicrobial compounds. In plants of Rosaceae, many constitutively synthesized isoflavonoids affecting microorganisms were identified. Bacterial multidrug efflux transporters which mediate resistance toward structurally unrelated compounds might confer tolerance to these phytoalexins. To prove this hypothesis, we cloned the acrAB locus from E. amylovora encoding a resistance nodulation division-type transport system. In Escherichia coli, AcrAB of E. amylovora conferred resistance to hydrophobic and amphiphilic toxins. An acrB-deficient E. amylovora mutant was impaired in virulence on apple rootstock MM 106. Furthermore, it was susceptible toward extracts of leaves of MM 106 as well as to the apple phytoalexins phloretin, naringenin, quercetin, and (+)-catechin. The expression of acrAB was determined using the promoterless reporter gene egfp. The acrAB operon was up-regulated in vitro by the addition of phloretin and naringenin. The promoter activity of acrR, encoding a regulatory protein involved in acrAB expression, was increased by naringenin. In planta, an induction of acrAB was proved by confocal laser scanning microscopy. Our results strongly suggest that the AcrAB transport system plays an important role as a protein complex required for virulence of E. amylovora in resistance toward apple phytoalexins and that it is required for successful colonization of a host plant.
authors.affiliation: School of Engineering and Sciences, International University Bremen, Campusring 1, 28759 Bremen, Germany.
authors.forename: Antje
authors.initials: A
authors.lastname: Burse
authors.forename: Helge
authors.initials: H
authors.lastname: Weingart
authors.forename: Matthias S
authors.initials: MS
authors.lastname: Ullrich
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004352:Drug Resistance, Microbial / Q000235:genetics; D044084:Erwinia amylovora / Q000472:pathogenicity*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D044950:Flavanones / Q000494:pharmacology; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D007113:Immunity, Innate / Q000235:genetics; D008074:Lipoproteins / Q000235:genetics / Q000378:metabolism; D027845:Malus / Q000737:chemistry / Q000382:microbiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009154:Mutation; D010641:Phenotype; D010693:Phloretin / Q000494:pharmacology; D010935:Plant Diseases / Q000382:microbiology*; D010936:Plant Extracts / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000187:drug effects; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid; D012717:Sesquiterpenes; D013729:Terpenes; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D014774:Virulence / Q000187:drug effects; D000094162:Phytoalexins
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D044950:Flavanones; D008074:Lipoproteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D010693:Phloretin; D010936:Plant Extracts; D012717:Sesquiterpenes; D013729:Terpenes; D000094162:Phytoalexins; C083497:AcrA protein, E coli; C083496:AcrB protein, E coli; C005273:naringenin