title: Different nitrogen sources modulate activity but not expression of glutamine synthetase in arbuscular mycorrhizal fungi.
abstract: Glutamine synthetase (GS) is a central enzyme of nitrogen metabolism that allows assimilation of nitrogen and biosynthesis of glutamine. We isolated the cDNA encoding GS from two arbuscular mycorrhizal fungi, Glomus mosseae (GmGln1) and Glomus intraradices (GiGln1). The deduced protein orthologues have a high degree of similarity (92%) with each other as well as with GSs from other fungi. GmGln1 was constitutively expressed during all stages of the fungal life cycle, i.e., spore germination, intraradical and extraradical mycelium. Feeding experiments with different nitrogen sources did not induce any change in the mRNA level of both genes independent of the symbiotic status of the fungus. However, GS activity of extraradical hypahe in G. intraradices was considerably modulated in response to different nitrogen sources. Thus, in a N re-supplementation time-course experiment, GS activity responded quickly to addition of nitrate, ammonium or glutamine. Re-feeding with ammonium produced a general increase in GS activity when compared with hyphae grown in nitrate as a sole N source.
authors.affiliation: Physiological Ecology of Plants Department, University of Tübingen, Auf der Morgenstelle 1, Tübingen 72076, Germany.
authors.forename: Magdalene
authors.initials: M
authors.lastname: Breuninger
authors.forename: Carmen G
authors.initials: CG
authors.lastname: Trujillo
authors.forename: Esther
authors.initials: E
authors.lastname: Serrano
authors.forename: Reinhard
authors.initials: R
authors.lastname: Fischer
authors.forename: Natalia
authors.initials: N
authors.lastname: Requena
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001483:Base Sequence; D018076:DNA, Complementary / Q000737:chemistry / Q000302:isolation & purification; D004271:DNA, Fungal / Q000737:chemistry / Q000302:isolation & purification; D020536:Enzyme Activators / Q000378:metabolism; D005658:Fungi / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D015966:Gene Expression Regulation, Fungal; D005974:Glutamate-Ammonia Ligase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism; D008969:Molecular Sequence Data; D025282:Mycelium / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D038821:Mycorrhizae / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D010802:Phylogeny; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012331:RNA, Fungal / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013172:Spores, Fungal / Q000201:enzymology / Q000235:genetics / Q000254:growth & development
chemical_list: D018076:DNA, Complementary; D004271:DNA, Fungal; D020536:Enzyme Activators; D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D012331:RNA, Fungal; D012333:RNA, Messenger; D005973:Glutamine; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen