The complete genome sequence of Xanthomonas albilineans provides new insights into the reductive genome evolution of the xylem-limited Xanthomonadaceae.
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.
Pieretti
Isabelle
I
CIRAD, UMR 385 BGPI, Campus international de Baillarguet, Montpellier, France. isabelle.pieretti@cirad.fr
Royer
Monique
M
Barbe
Valérie
V
Carrere
Sébastien
S
Koebnik
Ralf
R
Cociancich
Stéphane
S
Couloux
Arnaud
A
Darrasse
Armelle
A
Gouzy
Jérôme
J
Jacques
Marie-Agnès
MA
Lauber
Emmanuelle
E
Manceau
Charles
C
Mangenot
Sophie
S
Poussier
Stéphane
S
Segurens
Béatrice
B
Szurek
Boris
B
Verdier
Valérie
V
Arlat
Matthieu
M
Rott
Philippe
P
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*
D012329:RNA, Bacterial; D012335:RNA, Ribosomal