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Accueil du site → Doctorat → Suisse → Nutrient transport in the arbuscular mycorrhizal symbiosis : the regulation of nutrient transporters in Rhizophagus irregularis and its host plants populus trichocarpa and sorghum bicolor

University of Basel (2016)

Nutrient transport in the arbuscular mycorrhizal symbiosis : the regulation of nutrient transporters in Rhizophagus irregularis and its host plants populus trichocarpa and sorghum bicolor

Calabrese, Silvia.

Titre : Nutrient transport in the arbuscular mycorrhizal symbiosis : the regulation of nutrient transporters in Rhizophagus irregularis and its host plants populus trichocarpa and sorghum bicolor

Auteur : Calabrese, Silvia.

Université de soutenance : University of Basel

Grade : Doctor of Philosophy (PhD) 2016

Résumé partiel
In natural and agricultural ecosystems, arbuscular mycorrhizal (AM) fungi play a major role in plant nutrition. In AM symbiosis, the AM fungi extract mineral nutrients from the substrate and transfer them to the host plant. Inside the roots of the host plant, the intraradical hyphae form tree like structures (arbuscules) where the nutrients are released to the plant fungal interface. In return, the AM fungi receive carbohydrates from the plants. Specialized transport systems enable nutrient uptake from the substrate and translocation across membranes. As main components of organic molecules, phosphorus (P), nitrogen (N) and carbon (C) are of particular importance for symbiotic nutrient exchanges. This work is focused on a range of genes that encode proteins contributing to transport molecules (P, N and C nutrients) across cellular membranes in the plants Populus trichocarpa (poplar) and Sorghum bicolor (sorghum), and in the AM fungus Rhizophagus irregularis. In the AM fungus R. irregularis (formerly Glomus intraradices), we identified and characterized a novel functional ammonium transporter (AMT), GintAMT3. Quantification of transcript abundances in the extraradical mycelium (ERM) and the intraradical mycelium (IRM) during symbiosis with poplar and sorghum revealed that GintAMT3 was highly expressed in the IRM of AM roots. Phylogenetic analysis showed further, that the six glomeromycotan AMTs share high sequence similarity, but are distinct to AMTs of other fungal phyla. To functionaly analyze GintAMT3, we expressed GintAMT3 in a yeast deletion mutant devoid of all AMTs. The heterologous expression revealed that GintAMT3 is a low affinity transporter. Heterologous expression of GFP tagged GintAMT3 in yeast showed that GintAMT3 is localized in the plasma membrane and the vacuolar membrane. Further, we could show that expression of GinAMT3 is dependent on the N nutrition status and the fungal C status. Taken together, our data suggested that GintAMT3 is the main export carrier for ammonium at the arbuscular site.

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