title: Genomic insights into strategies used by Xanthomonas albilineans with its reduced artillery to spread within sugarcane xylem vessels.
abstract: BACKGROUND
  Xanthomonas albilineans causes leaf scald, a lethal disease of sugarcane. X. albilineans exhibits distinctive pathogenic mechanisms, ecology and taxonomy compared to other species of Xanthomonas. For example, this species produces a potent DNA gyrase inhibitor called albicidin that is largely responsible for inducing disease symptoms; its habitat is limited to xylem; and the species exhibits large variability. A first manuscript on the complete genome sequence of the highly pathogenic X. albilineans strain GPE PC73 focused exclusively on distinctive genomic features shared with Xylella fastidiosa-another xylem-limited Xanthomonadaceae. The present manuscript on the same genome sequence aims to describe all other pathogenicity-related genomic features of X. albilineans, and to compare, using suppression subtractive hybridization (SSH), genomic features of two strains differing in pathogenicity.
  
  
  RESULTS
  Comparative genomic analyses showed that most of the known pathogenicity factors from other Xanthomonas species are conserved in X. albilineans, with the notable absence of two major determinants of the "artillery" of other plant pathogenic species of Xanthomonas: the xanthan gum biosynthesis gene cluster, and the type III secretion system Hrp (hypersensitive response and pathogenicity). Genomic features specific to X. albilineans that may contribute to specific adaptation of this pathogen to sugarcane xylem vessels were also revealed. SSH experiments led to the identification of 20 genes common to three highly pathogenic strains but missing in a less pathogenic strain. These 20 genes, which include four ABC transporter genes, a methyl-accepting chemotaxis protein gene and an oxidoreductase gene, could play a key role in pathogenicity. With the exception of hypothetical proteins revealed by our comparative genomic analyses and SSH experiments, no genes potentially involved in any offensive or counter-defensive mechanism specific to X. albilineans were identified, supposing that X. albilineans has a reduced artillery compared to other pathogenic Xanthomonas species. Particular attention has therefore been given to genomic features specific to X. albilineans making it more capable of evading sugarcane surveillance systems or resisting sugarcane defense systems.
  
  
  CONCLUSIONS
  This study confirms that X. albilineans is a highly distinctive species within the genus Xanthomonas, and opens new perpectives towards a greater understanding of the pathogenicity of this destructive sugarcane pathogen.
authors.affiliation: CIRAD, UMR BGPI, F-34398 Montpellier Cedex 5, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Pieretti
authors.forename: Monique
authors.initials: M
authors.lastname: Royer
authors.forename: Valérie
authors.initials: V
authors.lastname: Barbe
authors.forename: Sébastien
authors.initials: S
authors.lastname: Carrere
authors.forename: Ralf
authors.initials: R
authors.lastname: Koebnik
authors.forename: Arnaud
authors.initials: A
authors.lastname: Couloux
authors.forename: Armelle
authors.initials: A
authors.lastname: Darrasse
authors.forename: Jérôme
authors.initials: J
authors.lastname: Gouzy
authors.forename: Marie-Agnès
authors.initials: MA
authors.lastname: Jacques
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Lauber
authors.forename: Charles
authors.initials: C
authors.lastname: Manceau
authors.forename: Sophie
authors.initials: S
authors.lastname: Mangenot
authors.forename: Stéphane
authors.initials: S
authors.lastname: Poussier
authors.forename: Béatrice
authors.initials: B
authors.lastname: Segurens
authors.forename: Boris
authors.initials: B
authors.lastname: Szurek
authors.forename: Valérie
authors.initials: V
authors.lastname: Verdier
authors.forename: Matthieu
authors.initials: M
authors.lastname: Arlat
authors.forename: Dean W
authors.initials: DW
authors.lastname: Gabriel
authors.forename: Philippe
authors.initials: P
authors.lastname: Rott
authors.forename: Stéphane
authors.initials: S
authors.lastname: Cociancich
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics; D018829:Adhesins, Bacterial / Q000235:genetics; D001483:Base Sequence; D002874:Chromosome Mapping; D016000:Cluster Analysis; D005798:Genes, Bacterial / Q000235:genetics; D016680:Genome, Bacterial / Q000235:genetics*; D015151:Immunoblotting; D055029:Inverted Repeat Sequences / Q000235:genetics; D008957:Models, Genetic; D008969:Molecular Sequence Data; D021141:Nucleic Acid Amplification Techniques / Q000379:methods; D010802:Phylogeny; D053038:Quorum Sensing / Q000235:genetics; D031786:Saccharum / Q000382:microbiology*; D017422:Sequence Analysis, DNA; D015398:Signal Transduction / Q000235:genetics; D013045:Species Specificity; D037521:Virulence Factors / Q000235:genetics*; D014974:Xanthomonas / Q000235:genetics / Q000472:pathogenicity*; D052584:Xylem / Q000382:microbiology*
chemical_list: D018528:ATP-Binding Cassette Transporters; D018829:Adhesins, Bacterial; D037521:Virulence Factors