Déterminisme moléculaire des interactions entre le champignon ectomycorhizien Laccaria bicolor S238N et des bactéries du sol

Abstract : Ectomycorrhizal fungi have a beneficial impact on tree nutrition and growth by forming symbiotic associations with roots. In their natural environment, they interact physically and metabolically with soil bacterial communities that are beneficial, neutral or antagonistic to the fungus. Since the 80ies, a specific interest has been given to bacterial strains that improve the formation of ectomycorrhizal symbiosis, so-called mycorrhiza helper bacteria. The strain Pseudomonas fluorescens BBc6R8 is particularly efficient to enhance the establishment of Douglas fir - Laccaria bicolor S238N mycorrhizal symbiosis, by improving the survival and the growth of the pre-symbiotic mycelium in soil. We have used both a global and a targeted approach to investigate the molecular mechanisms of this helper effect. In a first step, we have analysed, using an in vitro assay, the morphological and the transcriptomic responses of the ectomycorrhizal fungus to the presence of the helper bacteria at different time of the interaction. Then we have assessed the question of the specificity of the fungal response by studying the effect of non-helper bacterial strains on the fungal behaviour. Finally, we have focused on the role played by several key molecules in the interaction : thiamine, trehalose and the type III secretion system. We suggest that the bacterial strain would exert its helper effect through a combination of mechanisms: an improvement of the nutritional status of the fungus and a preparation of both the plant and the ectomycorrhizal fungus to the root infection.
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http://docnum.univ-lorraine.fr/prive/SCD_T_2007_0134_DEVEAU.pdf
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Submitted on : Thursday, March 29, 2018 - 10:49:31 AM
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Aurélie Deveau. Déterminisme moléculaire des interactions entre le champignon ectomycorhizien Laccaria bicolor S238N et des bactéries du sol. Sciences agricoles. Université Henri Poincaré - Nancy 1, 2007. Français. ⟨NNT : 2007NAN10134⟩. ⟨tel-01747014⟩

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