title: GintAMT3 - a Low-Affinity Ammonium Transporter of the Arbuscular Mycorrhizal Rhizophagus irregularis.
abstract: Nutrient acquisition and transfer are essential steps in the arbuscular mycorrhizal (AM) symbiosis, which is formed by the majority of land plants. Mineral nutrients are taken up by AM fungi from the soil and transferred to the plant partner. Within the cortical plant root cells the fungal hyphae form tree-like structures (arbuscules) where the nutrients are released to the plant-fungal interface, i.e., to the periarbuscular space, before being taken up by the plant. In exchange, the AM fungi receive carbohydrates from the plant host. Besides the well-studied uptake of phosphorus (P), the uptake and transfer of nitrogen (N) plays a crucial role in this mutualistic interaction. In the AM fungus Rhizophagus irregularis (formerly called Glomus intraradices), two ammonium transporters (AMT) were previously described, namely GintAMT1 and GintAMT2. Here, we report the identification and characterization of a newly identified R. irregularis AMT, GintAMT3. Phylogenetic analyses revealed high sequence similarity to previously identified AM fungal AMTs and a clear separation from other fungal AMTs. Topological analysis indicated GintAMT3 to be a membrane bound pore forming protein, and GFP tagging showed it to be highly expressed in the intraradical mycelium of a fully established AM symbiosis. Expression of GintAMT3 in yeast successfully complemented the yeast AMT triple deletion mutant (MATa ura3 mep1Δ mep2Δ::LEU2 mep3Δ::KanMX2). GintAMT3 is characterized as a low affinity transport system with an apparent Km of 1.8 mM and a V max of 240 nmol(-1) min(-1) 10(8) cells(-1), which is regulated by substrate concentration and carbon supply.
authors.affiliation: Department of Environmental Sciences, Botany, Zurich-Basel Plant Science Center, University of Basel Basel, Switzerland.
authors.forename: Silvia
authors.initials: S
authors.lastname: Calabrese
authors.affiliation: Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas Granada, Spain.
authors.forename: Jacob
authors.initials: J
authors.lastname: Pérez-Tienda
authors.affiliation: Faculty of Biology, Genetics, Ludwig-Maximilians-University Munich Planegg-Martinsried, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Ellerbeck
authors.affiliation: Agroécologie, AgroSup Dijon, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, Université Bourgogne Franche-Comté Dijon, France.
authors.forename: Christine
authors.initials: C
authors.lastname: Arnould
authors.affiliation: Agroécologie, AgroSup Dijon, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, Université Bourgogne Franche-Comté Dijon, France.
authors.forename: Odile
authors.initials: O
authors.lastname: Chatagnier
authors.affiliation: Department of Environmental Sciences, Botany, Zurich-Basel Plant Science Center, University of Basel Basel, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Boller
authors.affiliation: Faculty of Biology, Genetics, Ludwig-Maximilians-University Munich Planegg-Martinsried, Germany.
authors.forename: Arthur
authors.initials: A
authors.lastname: Schüßler
authors.affiliation: Faculty of Biology, Genetics, Ludwig-Maximilians-University Munich Planegg-Martinsried, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Brachmann
authors.affiliation: Agroécologie, AgroSup Dijon, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, Université Bourgogne Franche-Comté Dijon, France.
authors.forename: Daniel
authors.initials: D
authors.lastname: Wipf
authors.affiliation: Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas Granada, Spain.
authors.forename: Nuria
authors.initials: N
authors.lastname: Ferrol
authors.affiliation: Department of Environmental Sciences, Botany, Zurich-Basel Plant Science Center, University of Basel Basel, Switzerland.
authors.forename: Pierre-Emmanuel
authors.initials: PE
authors.lastname: Courty
keywords: ammonium transporter; arbuscular mycorrhizal fungi; extraradical mycelium; intraradical mycelium; low affinity transporter