title: The complete genome sequence of Xanthomonas albilineans provides new insights into the reductive genome evolution of the xylem-limited Xanthomonadaceae.
abstract: BACKGROUND
  The Xanthomonadaceae family contains two xylem-limited plant pathogenic bacterial species, Xanthomonas albilineans and Xylella fastidiosa. X. fastidiosa was the first completely sequenced plant pathogen. It is insect-vectored, has a reduced genome and does not possess hrp genes which encode a Type III secretion system found in most plant pathogenic bacteria. X. fastidiosa was excluded from the Xanthomonas group based on phylogenetic analyses with rRNA sequences.
  
  
  RESULTS
  The complete genome of X. albilineans was sequenced and annotated. X. albilineans, which is not known to be insect-vectored, also has a reduced genome and does not possess hrp genes. Phylogenetic analysis using X. albilineans genomic sequences showed that X. fastidiosa belongs to the Xanthomonas group. Order of divergence of the Xanthomonadaceae revealed that X. albilineans and X. fastidiosa experienced a convergent reductive genome evolution during their descent from the progenitor of the Xanthomonas genus. Reductive genome evolutions of the two xylem-limited Xanthomonadaceae were compared in light of their genome characteristics and those of obligate animal symbionts and pathogens.
  
  
  CONCLUSIONS
  The two xylem-limited Xanthomonadaceae, during their descent from a common ancestral parent, experienced a convergent reductive genome evolution. Adaptation to the nutrient-poor xylem elements and to the cloistered environmental niche of xylem vessels probably favoured this convergent evolution. However, genome characteristics of X. albilineans differ from those of X. fastidiosa and obligate animal symbionts and pathogens, indicating that a distinctive process was responsible for the reductive genome evolution in this pathogen. The possible role in genome reduction of the unique toxin albicidin, produced by X. albilineans, is discussed.
authors.affiliation: CIRAD, UMR 385 BGPI, Campus international de Baillarguet, Montpellier, France. isabelle.pieretti@cirad.fr
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: Stéphane
authors.initials: S
authors.lastname: Cociancich
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: Philippe
authors.initials: P
authors.lastname: Rott
mesh_terms: D019143:Evolution, Molecular; D016680:Genome, Bacterial / Q000235:genetics*; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D012329:RNA, Bacterial / Q000235:genetics; D012335:RNA, Ribosomal / Q000235:genetics; D044166:Xanthomonadaceae / Q000145:classification / Q000235:genetics*; D014974:Xanthomonas / Q000145:classification / Q000235:genetics*; D052584:Xylem / Q000382:microbiology*
chemical_list: D012329:RNA, Bacterial; D012335:RNA, Ribosomal