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Régulation de la symbiose endomycorhizienne par le phosphate

Coline Balzergue 1
1 Symbiose mycorhizienne et Signalisation cellulaire
LRSV - Laboratoire de Recherche en Sciences Végétales
Abstract : Most plants form root symbioses with arbuscular mycorrhizal (AM) fungi. AM fungi supply their host plants with water and minerals, especially phosphate. In return, they obtain carbohydrates from their hosts. Phosphate fertilization is known to have a negative impact on the symbiotic interaction, but the underlying mechanisms are not yet understood. We first showed that phosphate supply is able to almost totally inhibit the interaction at a very early stage, prior to the attachment of fungal hyphae to the root epidermis. This inhibition is linked to shoot phosphate contents and involves a systemic regulation. Then, we tried to identify mechanisms involved in the regulation of AM symbiosis by phosphate. Early signaling events were examined with a particular focus on root exudates. First, the importance of strigolactones in the regulation was tested. Strigolactones are rootsecreted compounds which stimulate fungal growth and metabolism. Strigolactone production is also systemically regulated by phosphate, and root exudates of phosphatereplete plants lack strigolactones. However, supplementation with exogenous strigolactones failed to restore root colonization under high phosphate supply. Moreover, the role of root exudates in general (not only strigolactones) in the regulation was addressed. Although root exudates contribute to the control of the interaction, additional regulatory mechanisms likely exist at the level of the root itself. Among several hypothetical regulatory mechanisms we tested whether phosphate could affect the ability of plants to recognize properly their fungal partners. To test this hypothesis we used two approaches. (i) Root cells are known to respond to AM fungi by oscillations of calcium concentrations in the nucleus. We did not find any effect of phosphate on this response. (ii) We also analyzed whether phosphate could modify plant gene expression in response to the fungus. Regardless of phosphate supply, plants are able to respond to the presence of fungus by the induction of defense-related and "symbiotic" genes. However, phosphate negatively affects the expression of some symbiotic genes, suggesting that plants are less able to respond to the fungus when they are not under phosphate starvation. Finally, other potential regulatory mechanisms (such as cell wall composition or an involvement of strigolactones role at the hormonal level) are proposed and discussed.
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https://tel.archives-ouvertes.fr/tel-00796089
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Submitted on : Friday, March 1, 2013 - 4:06:30 PM
Last modification on : Friday, January 10, 2020 - 9:10:17 PM
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Coline Balzergue. Régulation de la symbiose endomycorhizienne par le phosphate. Biologie végétale. Université Paul Sabatier - Toulouse III, 2012. Français. ⟨tel-00796089⟩

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