Mathieu Arlat

The complete genome sequence of Xanthomonas albilineans provides new insights into the reductive genome evolution of the xylem-limited Xanthomonadaceae

BackgroundThe 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.ResultsThe 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.ConclusionThe 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.

Draft Genome Sequence of the Flagellated Xanthomonas fuscans subsp. fuscans Strain CFBP 4884

ABSTRACT We report the draft genome sequence of the flagellated strain CFBP 4884 of Xanthomonas fuscans subsp. fuscans, which was isolated in an outbreak of common bacterial blight of beans along with non-flagellated strains. Comparative genomics will allow one to decipher the genomic diversity of strains cohabiting in epidemics.

Draft Genome Sequence of Xanthomonas axonopodis pv. allii Strain CFBP 6369

ABSTRACT We report here the draft genome sequence of Xanthomonas axonopodis pv. allii strain CFBP 6369, the causal agent of bacterial blight of onion. The draft genome has a size of 5,425,942 bp and a G+C content of 64.4%.

High-Quality Draft Genome Sequence of Xanthomonas alfalfae subsp. alfalfae Strain CFBP 3836

ABSTRACT We report the high-quality draft genome sequence of Xanthomonas alfalfae subsp. alfalfae strain CFBP 3836, the causal agent of bacterial leaf and stem spot in lucerne (Medicago sativa). Comparative genomics will help to decipher the mechanisms provoking disease and triggering the defense responses of this pathogen of the model legume Medicago truncatula.

High-Quality Draft Genome Sequences of Two Xanthomonas Pathotype Strains Infecting Aroid Plants

ABSTRACT We present here the draft genome sequences of bacterial pathogens of the Araceae family, Xanthomonas axonopodis pv. dieffenbachiae LMG 695 and Xanthomonas campestris pv. syngonii LMG 9055, differing in host range. A comparison between genome sequences will help understand the mechanisms involved in tissue specificity and adaptation to host plants.

Genome and transcriptome analysis to reveal adaptation to new environments and hosts

Pathovars of Xanthomonas are interesting working models for the analysis of mechanisms of adaptation and specialization to hosts, plant tissues, niches and environments. The understanding of such mechanisms is important on practical and academic points of view since they can help explain how emergence of new diseases or of diseases in new situations may occur. Four research groups belonging to the French Network on Xanthomonas (FNX) have recently focused on genome and transcriptome sequencing of several pathovars of Xanthomonas chosen for their adaptation particularities, in a project called “Xanthomix”. Xanthomonas strains attacking Anacardiaceae, citrus, crucifers, legumes or rice were selected to help understand adaptation processes: genetic structure revealing either convergence or divergence for causing a specific disease on a specific host ; host tissue specialization (xylem vs. mesophyll) ; virulence variation (broad vs. narrow host range); contrasted epidemic situation (endemic vs. epidemic). RNAseq experiments were performed on a large set of strains to determine the extent and the diversity of the hrp regulon. In addition, the RNAseq dataset is also being used to improve Xanthomonas genome annotation and gene prediction. Analysis of transcripts allowed us to scan for unknown specific and non-specific effectors as well as small non-coding RNAs and hypothesize new mechanisms that could be involved in adaptation to host and environment. (Texte integral)