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Interaction entre des mutants hrp d'Erwinia amylovora, agent du feu bactérien, le parent pathogène et la plante hôte : recherche de mécanismes modulant la compatibilité

Abstract : Erwinia amylovora is the causal agent of fire blight, a disease that affects Maloideae. This gammaproteobacteria requires a type three secretion system (T3SS) for its pathogenicity. Previous work has shown that avirulent hrp mutant strains of E. amylovora affected in regulatory functions (hrpL and hrpS) protect apple seedlings from developping fire blight symptoms. We investigated molecular mechanisms leading to this protection. In a first part of our work, we studied molecular responses of the protected plant, according to major defense pathways (salicylic acid, jasmonic acid, ethylene) and in the phenylpropanoid pathway. Results show that none of these pathways is particularly induced by Ea hrpL or Ea hrpS mutants. Then, the hypothesis of a direct effect of mutants on the wild type strain has been denied. We tried to trace differential transcripts and proteins between these bacteria through targeted and global approaches (targeted genes vs cDNA-AFLP). Results show that HrpL and HrpS are able to differentially regulate other genes that hrp genes : HrpL negatively regulates flagellar system, chemotaxis and genes related to GSP, and positively regulates one gene of T1SS and one OMP ; HrpS negatively regulates quorum sensing and positively regulates one gene implicated in the synthesis of ethylene. We were particularly interested in flagellar system of E. amylovora. An in silico analysis of flagellar genes led to the discovery that E. amylovora possesses two flagellar systems with distincts flagellins (32 vs 50KDa). The 32KDa flagellin, overexpressed in hrpL mutant, does not display the flg22 peptide classically implicated in elicitation and is not necessary for protection. On the whole, our work does not entirely explain the origin of the plant protection, induced by regulatory hrp mutants, nevertheless it provides new key information on E. amylovora and on the regulation of several genes during the interaction with the host plant.
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https://tel.archives-ouvertes.fr/tel-00455109
Contributor : Anne-Marie Plé <>
Submitted on : Tuesday, February 9, 2010 - 3:25:53 PM
Last modification on : Tuesday, March 17, 2020 - 3:10:42 AM
Long-term archiving on: : Friday, June 18, 2010 - 7:43:26 PM

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  • HAL Id : tel-00455109, version 1

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Sophie Cesbron. Interaction entre des mutants hrp d'Erwinia amylovora, agent du feu bactérien, le parent pathogène et la plante hôte : recherche de mécanismes modulant la compatibilité. Biologie végétale. Université d'Angers, 2009. Français. ⟨tel-00455109⟩

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