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PLANTS INTERACTING WITH OTHER ORGANISMS

Characterization of an Amino Acid Permease from the Endomycorrhizal Fungus Glomus mosseae^1,[W]

Dipartimento di Biologia Vegetale, Università di Torino, 10125 Torino, Italy (G.C., L.L., P.B.); Istituto per la Protezione delle Piante, Consiglio Nazionale delle Ricerche, 10125 Torino, Italy (P.B.); NWG Transport in der Mykorrhiza IZMB-Institut für Zelluläre und Molekulare Botanik, Bonn University, D–53115 Bonn, Germany (M.F.); and UMR INRA 1088/CNRS 5184/Université de Bourgogne Plante-Microbe-Environnement, F–21000 Dijon cedex, France (D.W.)

Arbuscular mycorrhizal (AM) fungi are capable of exploiting organic nitrogen sources, but the molecular mechanisms that control such an uptake are still unknown. Polymerase chain reaction-based approaches, bioinformatic tools, and a heterologous expression system have been used to characterize a sequence coding for an amino acid permease (GmosAAP1) from the AM fungus Glomus mosseae. The GmosAAP1 shows primary and secondary structures that are similar to those of other fungal amino acid permeases. Functional complementation and uptake experiments in a yeast mutant that was defective in the multiple amino acid uptake system demonstrated that GmosAAP1 is able to transport proline through a proton-coupled, pH- and energy-dependent process. A competitive test showed that GmosAAP1 binds nonpolar and hydrophobic amino acids, thus indicating a relatively specific substrate spectrum. GmosAAP1 mRNAs were detected in the extraradical fungal structures. Transcript abundance was increased upon exposure to organic nitrogen, in particular when supplied at 2 mM concentrations. These findings suggest that GmosAAP1 plays a role in the first steps of amino acid acquisition, allowing direct amino acid uptake from the soil and extending the molecular tools by which AM fungi exploit soil resources.

² These authors contributed equally to the article.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Luisa Lanfranco (luisa.lanfranco{at}unito.it).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.117820

^* Corresponding author; e-mail luisa.lanfranco{at}unito.it.

Received February 15, 2008; accepted March 11, 2008; published March 14, 2008.