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Applied and Environmental Microbiology, September 2007, p. 5523-5530, Vol. 73, No. 17
0099-2240/07/$08.00+0 doi:10.1128/AEM.00577-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
Substrate Specificity-Conferring Regions of the Nonribosomal Peptide Synthetase Adenylation Domains Involved in Albicidin Pathotoxin Biosynthesis Are Highly Conserved within the Species Xanthomonas albilineans
Adeline Renier,1
Eric Vivien,1
Stéphane Cociancich,1
Philippe Letourmy,2
Xavier Perrier,3
Philippe C. Rott,1 and
Monique Royer1*
UMR CIRAD-INRA-Montpellier SupAgro Biologie et Génétique des Interactions Plante-Parasite, Centre de Coopération Internationale en Recherche Agronomique pour le Développement, Campus International de Baillarguet,1 UPR Biostatistique,2 UPR Multiplication Végétative, Centre de Coopération Internationale en Recherche Agronomique pour le Développement, Avenue Agropolis, Montpellier, France3
Received 13 March 2007/ Accepted 3 July 2007
Albicidin is a pathotoxin produced by Xanthomonas albilineans, a xylem-invading pathogen that causes leaf scald disease of sugarcane. Albicidin is synthesized by a nonribosomal pathway via modular polyketide synthase and nonribosomal peptide synthetase (NRPS) megasynthases, and NRPS adenylation (A) domains are responsible for the recognition and activation of specific amino acid substrates. DNA fragments (0.5 kb) encoding the regions responsible for the substrate specificities of six albicidin NRPS A domains from 16 strains of X. albilineans representing the known diversity of this pathogen were amplified and sequenced. Polymorphism analysis of these DNA fragments at different levels (DNA, protein, and NRPS signature) showed that these pathogenicity loci were highly conserved. The conservation of these loci most likely reflects purifying selective pressure, as revealed by a comparison with the variability of nucleotide and amino acid sequences of two housekeeping genes (atpD and efp) of X. albilineans. Nevertheless, the 16 strains of X. albilineans were differentiated into several groups by a phylogenetic analysis of the nucleotide sequences corresponding to the NRPS A domains. One of these groups was representative of the genetic diversity previously found within the pathogen by random fragment length polymorphism and amplified fragment length polymorphism analyses. This group, which differed by three single synonymous nucleotide mutations, contained only four strains of X. albilineans that were all involved in outbreaks of sugarcane leaf scald. The amount of albicidin produced in vitro in agar and liquid media varied among the 16 strains of X. albilineans. However, no relationship among the amount of albicidin produced in vitro and the pathotypes and genetic diversity of the pathogen was found. The NRPS loci contributing to the synthesis of the primary structure of albicidin apparently are not involved in the observed pathogenicity differences among strains of X. albilineans.
* Corresponding author. Mailing address: UMR BGPI, CIRAD, TA A-54/K, Campus International de Baillarguet, 34398 Montpellier Cedex 5, France. Phone: 33 (0)4 99 62 48 44. Fax: 33 (0)4 99 62 48 08. E-mail: monique.royer{at}cirad.fr
Published ahead of print on 13 July 2007.
Applied and Environmental Microbiology, September 2007, p. 5523-5530, Vol. 73, No. 17
0099-2240/07/$08.00+0 doi:10.1128/AEM.00577-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
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