title: The ATP-dependent RNA helicase HrpB plays an important role in motility and biofilm formation in Xanthomonas citri subsp. citri.
abstract: BACKGROUND
  RNA helicases are enzymes that catalyze the separation of double-stranded RNA (dsRNA) using the free energy of ATP binding and hydrolysis. DEAD/DEAH families participate in many different aspects of RNA metabolism, including RNA synthesis, RNA folding, RNA-RNA interactions, RNA localization and RNA degradation. Several important bacterial DEAD/DEAH-box RNA helicases have been extensively studied. In this study, we characterize the ATP-dependent RNA helicase encoded by the hrpB (XAC0293) gene using deletion and genetic complementation assays. We provide insights into the function of the hrpB gene in Xanthomonas citri subsp. citri by investigating the roles of hrpB in biofilm formation on abiotic surfaces and host leaves, cell motility, host virulence of the citrus canker bacterium and growth in planta.
  
  
  RESULTS
  The hrpB gene is highly conserved in the sequenced strains of Xanthomonas. Mutation of the hrpB gene (∆hrpB) resulted in a significant reduction in biofilms on abiotic surfaces and host leaves. ∆hrpB also exhibited increased cell dispersion on solid medium plates. ∆hrpB showed reduced adhesion on biotic and abiotic surfaces and delayed development in disease symptoms when sprayed on susceptible citrus leaves. Quantitative reverse transcription-PCR assays indicated that deletion of hrpB reduced the expression of four type IV pili genes. The transcriptional start site of fimA (XAC3241) was determined using rapid amplification of 5'-cDNA Ends (5'RACE). Based on the results of fimA mRNA structure predictions, the fimA 5' UTR may contain three different loops. HrpB may be involved in alterations to the structure of fimA mRNA that promote the stability of fimA RNA.
  
  
  CONCLUSIONS
  Our data show that hrpB is involved in adherence of Xanthomonas citri subsp. citri to different surfaces. In addition, to the best of our knowledge, this is the first time that a DEAH RNA helicase has been implicated in the regulation of type IV pili in Xanthomonas.
authors.affiliation: Centro de Citricultura Sylvio Moreira/IAC, Rodovia Anhanguera Km 158, Cordeirópolis, SP, 13490-970, Brazil.|Universidade Estadual de Campinas/UNICAMP, Instituto de Biologia, P.O. Box 6010, Campinas, SP, 13083-970, Brazil.
authors.forename: Laís Moreira
authors.initials: LM
authors.lastname: Granato
authors.affiliation: Centro de Citricultura Sylvio Moreira/IAC, Rodovia Anhanguera Km 158, Cordeirópolis, SP, 13490-970, Brazil.
authors.forename: Simone Cristina
authors.initials: SC
authors.lastname: Picchi
authors.affiliation: Citrus Research and Educational Center, Department of Microbiology and Cell Science, University of Florida, IFAS, 700 Experiment Station Road, Lake Alfred, FL, 33850, USA.
authors.forename: Maxuel de Oliveira
authors.initials: Mde O
authors.lastname: Andrade
authors.affiliation: Centro de Citricultura Sylvio Moreira/IAC, Rodovia Anhanguera Km 158, Cordeirópolis, SP, 13490-970, Brazil.
authors.forename: Marco Aurélio
authors.initials: MA
authors.lastname: Takita
authors.affiliation: Centro de Citricultura Sylvio Moreira/IAC, Rodovia Anhanguera Km 158, Cordeirópolis, SP, 13490-970, Brazil.
authors.forename: Alessandra Alves
authors.initials: AA
authors.lastname: de Souza
authors.affiliation: Citrus Research and Educational Center, Department of Microbiology and Cell Science, University of Florida, IFAS, 700 Experiment Station Road, Lake Alfred, FL, 33850, USA.
authors.forename: Nian
authors.initials: N
authors.lastname: Wang
authors.affiliation: Centro de Citricultura Sylvio Moreira/IAC, Rodovia Anhanguera Km 158, Cordeirópolis, SP, 13490-970, Brazil. marcos@centrodecitricultura.br.
authors.forename: Marcos Antonio
authors.identifier: http://orcid.org/0000-0001-9780-3990
authors.initials: MA
authors.lastname: Machado
mesh_terms: D020121:5' Untranslated Regions; D001422:Bacterial Adhesion; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018441:Biofilms / Q000254:growth & development*; D002957:Citrus / Q000382:microbiology; D010861:Fimbriae, Bacterial / Q000235:genetics; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D010935:Plant Diseases / Q000382:microbiology; D018515:Plant Leaves / Q000382:microbiology; D020365:RNA Helicases / Q000235:genetics* / Q000378:metabolism*; D014774:Virulence; D014974:Xanthomonas / Q000201:enzymology / Q000472:pathogenicity* / Q000502:physiology*
chemical_list: D020121:5' Untranslated Regions; D001426:Bacterial Proteins; D020365:RNA Helicases
keywords: Biofilm; Citrus canker; RNA helicase; Type IV pili; Xanthomonas citri