Project

Pseudomonas; plant-beneficial; toxin; insecticidal; biological pest control; rhizosphere; molecular host-microbe interactions; insects; autofluorescent reporters

Lead
Lay summary
Insect pests and fungal diseases cause major damage to agricultural crops and in particular those affecting below-ground plant parts are very difficult to ward off with chemical pesticides. Plant protection with beneficial soil bacteria is an ecologically sound alternative. We study biocontrol strains of Pseudomonas fluorescens that colonize roots and suppress fungal plant diseases. We discovered that phylogenetically defined groups of these pseudomonads exhibit not only antifungal, but also potent oral and systemic insecticidal activity towards different lepidopteran pests. We identified a locus encoding a novel insect toxin we termed Fit for P. fluorescens insecticidal toxin. We demonstrated that the Fit toxin contributes substantially to insecticidal activity. In a first part of the present project, we aim at unravelling regulatory mechanisms that control Fit insect toxin expression, activity and transport during interaction of P. fluorescens with the insect host. A particular focus will be on Fit locus-specific regulators and their interconnection with global regulatory and signalling systems in the bacteria. The approach will include an activity mapping of the Fit toxin to identify domains that are indispensable for insect toxicity and toxin transport by the Fit locus-encoded protein secretion system. In addition, we will try to identify further traits contributing to anti-insect activity using a genomic expression library approach. In a second part, we will investigate two possibilities of exploiting the Fit toxin as a novel means for pest control, i.e. by treating plant surfaces with Fit producing pseudomonads and by controlled expression of the Fit toxin or active fragments thereof directly in the plant. The efficacy of the two methods in controlling important root and leaf pests will then be tested in plant assays. We expect that our discovery of potent oral anti-insect activity in plant-beneficial pseudomonads will open new possibilities for combined microbial pest and disease control, since these bacteria are very efficient, vector-independent below-ground plant parts colonizers. In a longer term perspective, the expression of the Fit toxin or active fragments in the plant may open up the possibility to develop new transgenic crops resistant to insect pests, offering an alternative to Bt crops.

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

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Background. Insect pests and fungal diseases cause major damage to agricultural crops and in particular those affecting below-ground plant parts are very difficult to ward off with chemical pesticides. Plant protection with beneficial soil bacteria is an ecologically sound alternative. We study biocontrol strains of Pseudomonas fluorescens that colonize roots and suppress fungal plant diseases. In the precedent project, we discovered that phylogenetically defined groups of these pseudomonads exhibit not only antifungal, but also potent oral and systemic insecticidal activity towards different lepidopteran pests and identified for the first time a locus encoding a novel insect toxin we termed Fit for P. fluorescens insecticidal toxin. We demonstrated that the Fit toxin contributes to anti-insect activity and obtained first insights into regulation of toxin production.Overall aim. In the first part of the project, we aim at unravelling regulatory mechanisms that control Fit insect toxin expression, activity and transport during interaction of P. fluorescens with the insect host and at identifying additional factors contributing to insecticidal activity. In the second part, we will investigate two possibilities of exploiting the Fit toxin as a novel means for pest control, i.e. by treating plant surfaces with Fit producing pseudomonads and by expressing Fit directly in the plant.Project keypoints. The following six tasks are envisaged. 1. Molecular analysis of locus-specific and global regulators and signals controlling Fit toxin expression in P. fluorescens during interaction with insects. 2. Investigation of Fit toxin transport and localization in P. fluorescens and implication of the Fit locus encoded protein secretion system. 3. Activity mapping of the Fit toxin to identify domains that are indispensable for insect toxicity and toxin transport. 4. Identification of additional traits contributing to anti-insect activity in plant-associated pseudomonads using a genomic expression library approach. 5. Evaluation of plant-colonizing Fit producing pseudomonads for the biological control of important root and leaf pests in plant assays. 6. Controlled expression of the Fit toxin or active fragments in Arabidopsis and evaluation of anti-pest properties of transgenic plants.Expected value. By studying the molecular basis of the regulation and activity of the Fit insect toxin and additional anti-insect factors during pseudomonad-insect interactions, we will generate fundamental new knowledge on the ecological role of insecticidal activity in plant-associated pseudomonads. Our discovery of potent oral anti-insect activity in plant-beneficial pseudomonads opens new possibilities for combined microbial pest and disease control, since these bacteria are very efficient, vector-independent below-ground plant parts colonizers. In a longer term perspective, the expression of the Fit toxin or active fragments in the plant may open up the possibility to develop new transgenic crops resistant to insect pests, offering an alternative to Bt crops.