title: Nitrogen transfer in the arbuscular mycorrhizal symbiosis.
abstract: Most land plants are symbiotic with arbuscular mycorrhizal fungi (AMF), which take up mineral nutrients from the soil and exchange them with plants for photosynthetically fixed carbon. This exchange is a significant factor in global nutrient cycles as well as in the ecology, evolution and physiology of plants. Despite its importance as a nutrient, very little is known about how AMF take up nitrogen and transfer it to their host plants. Here we report the results of stable isotope labelling experiments showing that inorganic nitrogen taken up by the fungus outside the roots is incorporated into amino acids, translocated from the extraradical to the intraradical mycelium as arginine, but transferred to the plant without carbon. Consistent with this mechanism, the genes of primary nitrogen assimilation are preferentially expressed in the extraradical tissues, whereas genes associated with arginine breakdown are more highly expressed in the intraradical mycelium. Strong changes in the expression of these genes in response to nitrogen availability and form also support the operation of this novel metabolic pathway in the arbuscular mycorrhizal symbiosis.
authors.affiliation: Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003, USA.
authors.forename: Manjula
authors.initials: M
authors.lastname: Govindarajulu
authors.forename: Philip E
authors.initials: PE
authors.lastname: Pfeffer
authors.forename: Hairu
authors.initials: H
authors.lastname: Jin
authors.forename: Jehad
authors.initials: J
authors.lastname: Abubaker
authors.forename: David D
authors.initials: DD
authors.lastname: Douds
authors.forename: James W
authors.initials: JW
authors.lastname: Allen
authors.forename: Heike
authors.initials: H
authors.lastname: Bücking
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Lammers
authors.forename: Yair
authors.initials: Y
authors.lastname: Shachar-Hill
mesh_terms: D000085:Acetates / Q000378:metabolism; D000596:Amino Acids; D001120:Arginine / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics; D018552:Daucus carota / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D005786:Gene Expression Regulation; D005800:Genes, Fungal / Q000235:genetics; D017343:Genes, Plant / Q000235:genetics; D008969:Molecular Sequence Data; D025282:Mycelium / Q000378:metabolism; D038821:Mycorrhizae / Q000235:genetics / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D013559:Symbiosis / Q000235:genetics
chemical_list: D000085:Acetates; D000596:Amino Acids; D004269:DNA, Bacterial; D009566:Nitrates; C036483:T-DNA; D001120:Arginine; D009584:Nitrogen