Christoph Keel,2 and
1Georg-August-University Göttingen, J.F. Blumenbach Institute of Zoology and Anthropology, Berliner Str. 28, 37073 Göttingen, Germany; 2Université de Lausanne, Département de Microbiologie Fondamentale, 1015 Lausanne, Switzerland; 3Université François Rabelais de Tours. EA 2106 Plant Biotechnology and Biomolecules, 31 Avenue Monge, 37200 Tours, France; 4University of Cologne, Institute of Zoology, Terrestrial Ecology and Rhizosphere Research, Zülpicher Straße 47 b, 50674 Köln, Germany
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Accepted 8 November 2010.
Plant health and fitness widely depend on interactions with soil microorganisms. Some bacteria such as pseudomonads can inhibit pathogens by producing antibiotics, and controlling these bacteria could help improve plant fitness. In the present study, we tested whether plants induce changes in the antifungal activity of root-associated bacteria as a response to root pathogens. We grew barley plants in a split-root system with one side of the root system challenged by the pathogen Pythium ultimum and the other side inoculated with the biocontrol strain Pseudomonas fluorescens CHA0. We used reporter genes to follow the expression of ribosomal RNA indicative of the metabolic state and of the gene phlA, required for production of 2,4-diacetylphloroglucinol, a key component of antifungal activity. Infection increased the expression of the antifungal gene phlA. No contact with the pathogen was required, indicating that barley influenced gene expression by the bacteria in a systemic way. This effect relied on increased exudation of diffusible molecules increasing phlA expression, suggesting that communication with rhizosphere bacteria is part of the pathogen response of plants. Tripartite interactions among plants, pathogens, and bacteria appear as a novel determinant of plant response to root pathogens.
© 2011 The American Phytopathological Society