title: A luminescent reporter evidences active expression of Ralstonia solanacearum type III secretion system genes throughout plant infection.
abstract: Although much is known about the signals that trigger transcription of virulence genes in plant pathogens, their prevalence and timing during infection are still unknown. In this work, we address these questions by analysing expression of the main pathogenicity determinants in the bacterial pathogen Ralstonia solanacearum. We set up a quantitative, non-invasive luminescent reporter to monitor in planta transcription from single promoters in the bacterial chromosome. We show that the new reporter provides a real-time measure of promoter output in vivo - either after re-isolation of pathogens from infected plants or directly in situ - and confirm that the promoter controlling exopolysaccharide (EPS) synthesis is active in bacteria growing in the xylem. We also provide evidence that hrpB, the master regulator of type III secretion system (T3SS) genes, is transcribed in symptomatic plants. Quantitative RT-PCR assays demonstrate that hrpB and type III effector transcripts are abundant at late stages of plant infection, suggesting that their function is required throughout disease. Our results challenge the widespread view in R. solanacearum pathogenicity that the T3SS, and thus injection of effector proteins, is only active to manipulate plant defences at the first stages of infection, and that its expression is turned down when bacteria reach high cell densities and EPS synthesis starts.
authors.affiliation: Department Genètica, Universitat de Barcelona and Centre de Recerca Agrigenòmica (IRTA-CSIC-UAB-UB) Edifici CRAG, Campus UAB, 08193 Bellaterra, Catalonia, Spain.
authors.forename: Freddy
authors.initials: F
authors.lastname: Monteiro
authors.affiliation: INRA, CNRS - Laboratoire des Interactions Plantes Micro-organismes (LIPM), UMR 441/2594, 31326 Castanet Tolosan, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Genin
authors.affiliation: Department Genètica, Universitat de Barcelona and Centre de Recerca Agrigenòmica (IRTA-CSIC-UAB-UB) Edifici CRAG, Campus UAB, 08193 Bellaterra, Catalonia, Spain.
authors.forename: Irene
authors.initials: I
authors.lastname: van Dijk
authors.affiliation: Department Genètica, Universitat de Barcelona and Centre de Recerca Agrigenòmica (IRTA-CSIC-UAB-UB) Edifici CRAG, Campus UAB, 08193 Bellaterra, Catalonia, Spain.
authors.forename: Marc
authors.initials: M
authors.lastname: Valls
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D058947:Bacterial Secretion Systems; D058948:Cell Tracking / Q000379:methods*; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D008156:Luciferases / Q000235:genetics* / Q000378:metabolism; D018551:Solanum lycopersicum / Q000382:microbiology*; D010935:Plant Diseases / Q000382:microbiology*; D043368:Ralstonia solanacearum / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems; D008156:Luciferases