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Applied and Environmental Microbiology, July 2005, p. 3778-3785, Vol. 71, No. 7
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.7.3778-3785.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Changes in Race-Specific Virulence in Pseudomonas syringae pv. phaseolicola Are Associated with a Chimeric Transposable Element and Rare Deletion Events in a Plasmid-Borne Pathogenicity Island

Luis A. Rivas,^1, John Mansfield,² George Tsiamis,^2,3, Robert W. Jackson,⁴ and Jesús Murillo^1*

Laboratorio de Patología Vegetal, Departamento de Producción Agraria, Escuela Técnica Superior de Ingenieros Agrónomos, Universidad Pública de Navarra, 31006 Pamplona, Spain,¹ Department of Agricultural Sciences, Imperial College, Wye Campus, Ashford, Kent TN25 5AH, United Kingdom,² Department of Environmental and Natural Resources Management, University of Ioannina, 2 Seferi St., 30100 Agrinio, Greece,³ Centre for Research in Plant Science, University of the West of England, Coldharbour Lane, Frenchay, Bristol BS16 1QY, United Kingdom⁴

Received 10 September 2004/ Accepted 19 January 2005

Virulence for bean and soybean is determined by effector genes in a plasmid-borne pathogenicity island (PAI) in race 7 strain 1449B of Pseudomonas syringae pv. phaseolicola. One of the effector genes, avrPphF, confers either pathogenicity, virulence, or avirulence depending on the plant host and is absent from races 2, 3, 4, 6, and 8 of this pathogen. Analysis of cosmid clones and comparison of DNA sequences showed that the absence of avrPphF from strain 1448A is due to deletion of a continuous 9.5-kb fragment. The remainder of the PAI is well conserved in strains 1448A and 1449B. The left junction of the deleted region consists of a chimeric transposable element generated from the fusion of homologs of IS1492 from Pseudomonas putida and IS1090 from Ralstonia eutropha. The borders of the deletion were conserved in 66 P. syringae pv. phaseolicola strains isolated in different countries and representing the five races lacking avrPphF. However, six strains isolated in Spain had a 10.5-kb deletion that extended 1 kb further from the right junction. The perfect conservation of the 28-nucleotide right repeat of the IS1090 homolog in the two deletion types and in the other 47 insertions of the IS1090 homolog in the 1448A genome strongly suggests that the avrPphF deletions were mediated by the activity of the chimeric mobile element. Our data strongly support a clonal origin for the races of P. syringae pv. phaseolicola lacking avrPphF.

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* Corresponding author. Mailing address: Laboratorio de Patología Vegetal, Departamento de Producción Agraria, Escuela Técnica Superior de Ingenieros Agrónomos, Universidad Pública de Navarra, 31006 Pamplona, Spain. Phone: 34 948 169133. Fax: 34 948 169732. E-mail: jesus{at}unavarra.es.

Present address: Centro de Astrobiología (CSIC-INTA), Crta. de Ajalvir, Km 4, 28850 Torrejón de Ardoz, Madrid, Spain.

Present address: Department of Environmental and Natural Resources Management, University of Ioannina, 2 Seferi St., 30100 Agrinio, Greece.

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Applied and Environmental Microbiology, July 2005, p. 3778-3785, Vol. 71, No. 7
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.7.3778-3785.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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