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During Infection of Its Host, the Plant Pathogen Ralstonia solanacearum Naturally Develops a State of Competence and Exchanges Genetic Material

¹Laboratoire d'Ecologie Microbienne du Sol, UMR CNRS 5557, Batiment 741, Université Lyon I, 43 bd du 11 Novembre 1918, F-69622 Villeurbanne Cedex, France; ²Department of Microbial Ecology, Lund University, Ecology Building, SE-223 62 Lund, Sweden; ³Laboratoire de Biologie Moléculaire des Relations Plantes-Microorganismes, INRA/CNRS, 31326 Castanet-Tolosan, France

In this work we investigated the ability of the plant pathogen Ralstonia solanacearum to develop a state of competence in planta and to be genetically transformed during the infection process. Tomato plants infected with R. solanacearum GMI1000 were inoculated with plasmid DNA. R. solanacearum clones expressing the marker gene were selected only during the period of time that bacteria were actively multiplying inside the plant vessels. Moreover, experiments in which R. solanacearum strains harboring different marker genes were co-inoculated into the plant demonstrated that infecting bacterial strains exchange genetic information in planta by a mechanism that is likely to be transformation. To our knowledge, these results constitute the first demonstration of soil microorganisms developing a state of competence in planta. The biotechnological implications of this result will be discussed.

Additional keywords: genetic transfer.