title: NADP-dependent glutamate dehydrogenase: a dispensable function in ectomycorrhizal fungi.
abstract: There is much controversy on the contribution of NADP-dependent glutamate dehydrogenase (NADP-GDH) in NH4+ assimilation in ectomycorrhizal (ECM) fungi and ectomycorrhizas. Experiments reported here provide information on the dispensability of NADP-GDH in various ectomycorrhizal isolates. Glutamate dehydrogenase and glutamine synthetase (GS) enzyme activities were measured on mycelia grown under various nitrogen (N) conditions. The contribution of GDH in ammonium assimilation was further estimated by following 15N incorporation from (15NH4)2SO4 into glutamate, when GS was inhibited by phosphinothricin. Finally, gene amplification on cDNA and genomic DNA was performed using degenerated primers. Two groups of fungi could be distinguished. The GDH+ fungi include Hebeloma cylindrosporum-like fungi, which possess a functional NADP-GDH. The GDH- fungi include Paxillus involutus-like fungi for which the NADP-GDH activity, as well as the GDHA transcripts, were not detected, whatever the growth condition. All the results are consistent with the dispensability of the NADP-GDH function in ECM fungi, suggesting a minor role in ammonium assimilation in ectomycorrhizal fungi. We hypothesize that the lack of a functional NADP-GDH could be an evolutive adaptation in relation to the ecological niche of ECM fungi, rather than a transitional regulation in response to changes in N contents of the extracellular medium.
authors.affiliation: IFR 110, UMR INRA/UHP 1136 Interactions Arbres Micro-organismes, Université Henri Poincaré- Nancy I, Faculté des Sciences et Techniques BP239, F-54506 Vandoeuvre-les-Nancy Cedex, France.
authors.forename: Mélanie
authors.initials: M
authors.lastname: Morel
authors.forename: Marc
authors.initials: M
authors.lastname: Buée
authors.forename: Michel
authors.initials: M
authors.lastname: Chalot
authors.forename: Annick
authors.initials: A
authors.lastname: Brun
mesh_terms: D000222:Adaptation, Physiological; D018086:Glutamate Dehydrogenase (NADP+) / Q000378:metabolism / Q000502:physiology*; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism / Q000494:pharmacology; D007700:Kinetics; D038821:Mycorrhizae / Q000201:enzymology*; D009584:Nitrogen / Q000378:metabolism; D009587:Nitrogen Isotopes; D010802:Phylogeny; D000644:Quaternary Ammonium Compounds / Q000378:metabolism / Q000494:pharmacology
chemical_list: D009587:Nitrogen Isotopes; D000644:Quaternary Ammonium Compounds; D018698:Glutamic Acid; D018086:Glutamate Dehydrogenase (NADP+); D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen