JXB Advance Access originally published online on February 24, 2007
Journal of Experimental Botany 2007 58(6):1485-1495; doi:10.1093/jxb/erm010
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© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)
RESEARCH PAPER |
Pseudomonas brassicacearum strain Am3 containing 1-aminocyclopropane-1-carboxylate deaminase can show both pathogenic and growth-promoting properties in its interaction with tomato
1All-Russia Research Institute for Agricultural Microbiology (ARRIAM), Podbelskogo Sh., 3, Pushkin-8, 196608, St-Petersburg, Russian Federation
2Department of Biological Sciences, University of Lancaster, Lancaster LA1 4YQ, UK
3Department of Biology, University of Waterloo, Waterloo, ON, Canada N2L 3G1
* To whom correspondence should be addressed. E-mail: belimov{at}rambler.ru
The role of bacterial 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity in the interaction between tomato (Lycopersicon esculentum=Solanum lycopersicum) and Pseudomonas brassicacearum was studied in different strains. The phytopathogenic strain 520-1 possesses ACC deaminase activity, an important trait of plant growth-promoting rhizobacteria (PGPR) that stimulates root growth. The ACC-utilizing PGPR strain Am3 increased in vitro root elongation and root biomass of soil-grown tomato cv. Ailsa Craig at low bacterial concentrations (106 cells ml–1 in vitro and 106 cells g–1 soil) but had negative effects on in vitro root elongation at higher bacterial concentrations. A mutant strain of Am3 (designated T8-1) that was engineered to be ACC deaminase deficient failed to promote tomato root growth in vitro and in soil. Although strains T8-1 and 520-1 inhibited root growth in vitro at higher bacterial concentrations (>106 cells ml–1), they did not cause disease symptoms in vitro after seed inoculation, or in soil supplemented with bacteria. All the P. brassicacearum strains studied caused pith necrosis when stems or fruits were inoculated with a bacterial suspension, as did the causal organism of this disease (P. corrugata 176), but the non-pathogenic strain Pseudomonas sp. Dp2 did not. Strains Am3 and T8-1 were marked with antibiotic resistance and fluorescence to show that bacteria introduced to the nutrient solution or on seeds in vitro, or in soil were capable of colonizing the root surface, but were not detected inside root tissues. Both strains showed similar colonization ability either on root surfaces or in wounded stems. The results suggest that bacterial ACC deaminase of P. brassicacearum Am3 can promote growth in tomato by masking the phytopathogenic properties of this bacterium.
Key words: ACC deaminase, colonization, ethylene, GFP, PGPR, phytopathogen, plant–bacteria interactions, Pseudomonas, rhizosphere, tomato
Present address: Department of Pathology and Laboratory Medicine, UCLA David Geffen School of Medicine (71-295 CHS), 650 Charles E. Young Drive South, Los Angeles, CA 90095, USA. Received 13 November 2006; Revised 31 December 2006 Accepted 5 January 2007
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