title: Proteomic comparison of Ralstonia solanacearum strains reveals temperature dependent virulence factors.
abstract: BACKGROUND
  Ralstonia solanacearum, the causal agent of bacterial wilt, is a genetically diverse bacterial plant pathogen present in tropical and subtropical regions of the world that infects more than 200 plant species, including economically important solanaceous crops. Most strains of R. solanacearum are only pathogenic at temperatures between 25 to 30°C with strains that can cause disease below 20°C considered a threat to agriculture in temperate areas. Identifying key molecular factors that distinguish strains virulent at cold temperatures from ones that are not is needed to develop effective management tools for this pathogen. We compared protein profiles of two strains virulent at low temperature and two strains not virulent at low temperature when incubated in the rhizosphere of tomato seedlings at 30 and 18°C using quantitative 2D DIGE gel methods. Spot intensities were quantified and compared, and differentially expressed proteins were sequenced and identified by mass spectrometry (MS/MS).
  
  
  RESULTS
  Four hundred and eighteen (418) differentially expressed protein spots sequenced produced 101 unique proteins. The identified proteins were classified in the Gene Ontology biological processes categories of metabolism, cell processes, stress response, transport, secretion, motility, and virulence. Identified virulence factors included catalase (KatE), exoglucanase A (ChbA), drug efflux pump, and twitching motility porin (PilQ). Other proteins identified included two components of a putative type VI secretion system. We confirmed differential expression of 13 candidate genes using real time PCR techniques. Global regulators HrpB and HrpG also had temperature dependent expression when quantified by real time PCR.
  
  
  CONCLUSIONS
  The putative involvement of the identified proteins in virulence at low temperature is discussed. The discovery of a functional type VI secretion system provides a new potential virulence mechanism to explore. The global regulators HrpG and HrpB, and the protein expression profiles identified suggest that virulence at low temperatures can be partially explained by differences in regulation of virulence factors present in all the strains.
authors.forename: Ana M
authors.initials: AM
authors.lastname: Bocsanczy
authors.forename: Ute C M
authors.initials: UC
authors.lastname: Achenbach
authors.forename: Arianna
authors.initials: A
authors.lastname: Mangravita-Novo
authors.forename: Marjorie
authors.initials: M
authors.lastname: Chow
authors.affiliation: Department of Plant Pathology, University of Florida, IFAS, Mid-Florida Research and Education Center, 2725 Binion Rd,, Apopka, FL 32703, USA. djn@ufl.edu.
authors.forename: David J
authors.initials: DJ
authors.lastname: Norman
mesh_terms: D001692:Biological Transport; D019295:Computational Biology; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D020543:Proteome; D040901:Proteomics / Q000379:methods; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D043368:Ralstonia solanacearum / Q000235:genetics / Q000378:metabolism*; D013312:Stress, Physiological / Q000235:genetics; D013696:Temperature; D014774:Virulence / Q000235:genetics; D037521:Virulence Factors / Q000235:genetics
chemical_list: D020543:Proteome; D012333:RNA, Messenger; D037521:Virulence Factors
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