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Microdomaines ordonnés de la membrane plasmique végétale : caractérisation et rôle dans la signalisation associée à la défense

Abstract : Recent studies have shown the existence of lateral sub-compartmentalization of plant plasmamembrane similar to that of animal cells and yeasts. The aim of this thesis was to provide newelements to characterize this compartmentalization (physical properties of specific domains,mechanisms of their formation, determination of their size, etc...) and to study its role in thephysiology of plant cells.The development spectral confocal microscopy coupled with the use of an environment-sensitiveprobe enabled to obtain the first description at the submicron scale of plasma membrane organizationinto domains exhibiting various physical properties. These domains coexist at the plasma membranesurface of tobacco suspension cells as well as the membrane of vesicles composed of models lipids orcell plasma membrane lipids, purified plasma membrane vesicles, and protoplasts. However,differences in the lateral organization observed in these membranes have shown the importance ofphytosterols which are, through specific interactions with neighboring plant lipids such as GIPCs,essential for local formation of ordered domains. The huge diversity of plant lipids drives thecompartmentalization of the plasma membrane allowing the dynamic segregation of membranecomponents. Sterols greatly increase membrane order, whereas proteins tends to decrease it.Cytoskeleton and cell wall do alter neither presence nor organization of ordered domains of the plasmamembrane. We have also shown that the organization of these domains is transiently modified duringthe early stages of defense signaling cascade. In fact, we have identified changes in overall physicalproperties and fine lateral organization of the membrane caused by various elicitors of defensereactions, including cryptogein, a protein secreted by the oomycete Phytophthora cryptogea. We haveshown that these changes are a generic element of defense signaling cascade and depend onphosphorylation processes; oxidative burst being also a major actor of the control of the increase ofmembrane order observed during the very early stages of the signalling process. Cryptogein, whichexhibits the particular ability to trap sterols, also showed a specific capacity to increase membranefluidity and amplify the intensity of the signalling cascade, as measured by the production of reactiveoxygen species.These results open new perspectives in the understanding of cell-elicitin interactions and provide anew view on the central role of sterol composition in the lateral organization of plant plasmamembrane. They also identify membrane dynamics as a new player in the signalling cascade occurringduring plant defense.
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Kevin Grosjean. Microdomaines ordonnés de la membrane plasmique végétale : caractérisation et rôle dans la signalisation associée à la défense. Sciences de la Terre. Université de Bourgogne, 2015. Français. ⟨NNT : 2015DIJOS089⟩. ⟨tel-01661600⟩

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