Potential Role of Pathogen Signaling in Multitrophic Plant-Microbe Interactions Involved in Disease Protection

Duffy, B.; Keel, Christoph; Défago, Geneviève

doi:10.1128/aem.70.3.1836-1842.2004

Cited by 98 publications

(56 citation statements)

References 67 publications

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“…Therefore, more phlD genotypes and their respective DAPG-deficient mutants need to be tested to more conclusively assess the contribution of the antibiotic DAPG in the natural soil suppressiveness to Fusarium wilt disease. Furthermore, DAPG biosynthesis may also have been repressed by specific environmental conditions (Duffy and Défago, 1999) or by fusaric acid ( Figure 5; Notz et al, 2002;Duffy et al, 2004), a phytotoxin produced by pathogenic F. oxysporum and non-pathogenic F. oxysporum strain Fo47 (Schouten et al, 2004). However, given that also phenazine production can be repressed by fusaric acid (Van Rij et al, 2004, it seems unlikely that this phytotoxin played a major role in the multitrophic interactions occurring in the biocontrol assays.…”

Section: Discussionmentioning

confidence: 99%

Phenazine antibiotics produced by fluorescent pseudomonads contribute to natural soil suppressiveness to Fusarium wilt

et al. 2009

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Natural disease-suppressive soils provide an untapped resource for the discovery of novel beneficial microorganisms and traits. For most suppressive soils, however, the consortia of microorganisms and mechanisms involved in pathogen control are unknown. To date, soil suppressiveness to Fusarium wilt disease has been ascribed to carbon and iron competition between pathogenic Fusarium oxysporum and resident non-pathogenic F. oxysporum and fluorescent pseudomonads. In this study, the role of bacterial antibiosis in Fusarium wilt suppressiveness was assessed by comparing the densities, diversity and activity of fluorescent Pseudomonas species producing 2,4-diacetylphloroglucinol (DAPG) (phlD+) or phenazine (phzC+) antibiotics. The frequencies of phlD+ populations were similar in the suppressive and conducive soils but their genotypic diversity differed significantly. However, phlD genotypes from the two soils were equally effective in suppressing Fusarium wilt, either alone or in combination with non-pathogenic F. oxysporum strain Fo47. A mutant deficient in DAPG production provided a similar level of control as its parental strain, suggesting that this antibiotic does not play a major role. In contrast, phzC+ pseudomonads were only detected in the suppressive soil. Representative phzC+ isolates of five distinct genotypes did not suppress Fusarium wilt on their own, but acted synergistically in combination with strain Fo47. This increased level of disease suppression was ascribed to phenazine production as the phenazine-deficient mutant was not effective. These results suggest, for the first time, that redox-active phenazines produced by fluorescent pseudomonads contribute to the natural soil suppressiveness to Fusarium wilt disease and may act in synergy with carbon competition by resident non-pathogenic F. oxysporum.

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Section: Discussionmentioning

confidence: 99%

Phenazine antibiotics produced by fluorescent pseudomonads contribute to natural soil suppressiveness to Fusarium wilt

et al. 2009

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“…Fusarium spp. are common soil fungi, which can have important roles not only as plant pathogens, but also as saprotrophic competitors of other pathogenic fungi (Duffy et al, 2004;Yergeau et al, 2005). In this study, the density of Fusarium spp., as judged by quantitative real-time PCR targeting the 18S-rRNA gene, was significantly reduced in the rhizosphere of the mycorrhizal plant (F. rubra) exposed to elevated atmospheric CO 2 concentration.…”

Section: Effects Of Elevated Co 2 On Fungal Communitiesmentioning

confidence: 99%

Specific rhizosphere bacterial and fungal groups respond differently to elevated atmospheric CO2

2009

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Soil community responses to increased atmospheric CO 2 concentrations are expected to occur mostly through interactions with changing vegetation patterns and plant physiology. To gain insight into the effects of elevated atmospheric CO 2 on the composition and functioning of microbial communities in the rhizosphere, Carex arenaria (a non-mycorrhizal plant species) and Festuca rubra (a mycorrhizal plant species) were grown under defined atmospheric conditions with either ambient (350 p.p.m.) or elevated (700 p.p.m.) CO 2 concentrations. PCR-DGGE (PCR-denaturing gradient gel electrophoresis) and quantitative-PCR were carried out to analyze, respectively, the structure and abundance of the communities of actinomycetes, Fusarium spp., Trichoderma spp., Pseudomonas spp., Burkholderia spp. and Bacillus spp. Responses of specific functional groups, such as phloroglucinol, phenazine and pyrrolnitrin producers, were also examined by quantitative-PCR, and HPLC (high performance liquid chromatography) was employed to assess changes in exuded sugars in the rhizosphere. Multivariate analysis of group-specific community profiles showed disparate responses to elevated CO 2 for the different bacterial and fungal groups examined, and these responses were dependent on plant type and soil nutrient availability. Within the bacterial community, the genera Burkholderia and Pseudomonas, typically known as successful rhizosphere colonizers, were significantly influenced by elevated CO 2 , whereas the genus Bacillus and actinomycetes, typically more dominant in bulk soil, were not. Total sugar concentrations in the rhizosphere also increased in both plants in response to elevated CO 2 . The abundances of phloroglucinol-, phenazine-and pyrrolnitrin-producing bacterial communities were also influenced by elevated CO 2 , as was the abundance of the fungal genera Fusarium and Trichoderma.

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“…Fusaric acid produced by Fusarium was shown to be the fungal metabolite that specifically repressed DAPG biosynthesis (Duffy and Défago 1997;Notz et al 2002): blocking fusaric acid production in Fusarium by addition of zinc relieved repression of the phlA gene and improved the activity of strain CHA0. Subsequent studies showed that among a collection of genotypically different DAPG-producing Pseudomonas strains, several were relatively insensitive to fusaric acid-mediated repression of DAPG biosynthesis (Duffy et al 2004).…”

Section: Interference With the Biosynthesis Of Antimicrobial Compoundmentioning

confidence: 99%

The rhizosphere: a playground and battlefield for soilborne pathogens and beneficial microorganisms

et al. 2008

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The rhizosphere is a hot spot of microbial interactions as exudates released by plant roots are a main food source for microorganisms and a driving force of their population density and activities. The rhizosphere harbors many organisms that have a neutral effect on the plant, but also attracts organisms that exert deleterious or beneficial effects on the plant. Microorganisms that adversely affect plant growth and health are the pathogenic fungi, oomycetes, bacteria and nematodes. Most of the soilborne pathogens are adapted to grow and survive in the bulk soil, but the rhizosphere is the playground and infection court where the pathogen establishes a parasitic relationship with the plant. The rhizosphere is also a battlefield where the complex rhizosphere community, both microflora and microfauna, interact with pathogens and influence the outcome of pathogen infection. A wide range of microorganisms are beneficial to the plant and include nitrogen-fixing bacteria, endo-and ectomycorrhizal fungi, and plant growth-promoting bacteria and fungi. This review focuses on the population dynamics and activity of soilborne pathogens and beneficial microorganisms. Specific attention is given to mechanisms involved in the tripartite interactions between beneficial microorganisms, pathogens and the plant. We also discuss how agricultural practices affect pathogen and antagonist populations and how these practices can be adopted to promote plant growth and health.

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Potential Role of Pathogen Signaling in Multitrophic Plant-Microbe Interactions Involved in Disease Protection

Cited by 98 publications

References 67 publications

Phenazine antibiotics produced by fluorescent pseudomonads contribute to natural soil suppressiveness to Fusarium wilt

Phenazine antibiotics produced by fluorescent pseudomonads contribute to natural soil suppressiveness to Fusarium wilt

Specific rhizosphere bacterial and fungal groups respond differently to elevated atmospheric CO2

The rhizosphere: a playground and battlefield for soilborne pathogens and beneficial microorganisms

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