title: Shoot- and root-borne cytokinin influences arbuscular mycorrhizal symbiosis.
abstract: The arbuscular mycorrhizal (AM) symbiosis is functionally important for the nutrition and growth of most terrestrial plants. Nearly all phytohormones are employed by plants to regulate the symbiosis with AM fungi, but the regulatory role of cytokinin (CK) is not well understood. Here, we used transgenic tobacco (Nicotiana tabacum) with a root-specific or constitutive expression of CK-degrading CKX genes and the corresponding wild-type to investigate whether a lowered content of CK in roots or in both roots and shoots influences the interaction with the AM fungus Rhizophagus irregularis. Our data indicates that shoot CK has a positive impact on AM fungal development in roots and on the root transcript level of an AM-responsive phosphate transporter gene (NtPT4). A reduced CK content in roots caused shoot and root growth depression following AM colonization, while neither the uptake of phosphorus or nitrogen nor the root transcript levels of NtPT4 were significantly affected. This suggests that root CK may restrict the C availability from the roots to the fungus thus averting parasitism by AM fungi. Taken together, our study indicates that shoot- and root-borne CK have distinct roles in AM symbiosis. We propose a model illustrating how plants may employ CK to regulate nutrient exchange with the ubiquitous AM fungi.
authors.affiliation: Functional Biodiversity, Dahlem Centre of Plant Sciences, Institute of Biology, Freie Universität Berlin, Königin-Luise-Straße 1-3, 14195, Berlin, Germany. m.p.rebecacosme@uu.nl.|Department of Plant Propagation, Leibniz Institute of Vegetable and Ornamental Crops, Kühnhäuser Straße 101, 99090, Erfurt-Kühnhausen, Germany. m.p.rebecacosme@uu.nl.|Plant-Microbe Interactions, Department of Biology, Faculty of Science, Utrecht University, PO Box 800.56, 3508 TB, Utrecht, The Netherlands. m.p.rebecacosme@uu.nl.
authors.forename: Marco
authors.initials: M
authors.lastname: Cosme
authors.affiliation: Applied Genetics, Dahlem Center of Plant Sciences, Freie Universität Berlin, Albrecht-Thaer-Weg 6, 14195, Berlin, Germany.
authors.forename: Eswarayya
authors.initials: E
authors.lastname: Ramireddy
authors.affiliation: Department of Plant Propagation, Leibniz Institute of Vegetable and Ornamental Crops, Kühnhäuser Straße 101, 99090, Erfurt-Kühnhausen, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Franken
authors.affiliation: Applied Genetics, Dahlem Center of Plant Sciences, Freie Universität Berlin, Albrecht-Thaer-Weg 6, 14195, Berlin, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Schmülling
authors.affiliation: Functional Biodiversity, Dahlem Centre of Plant Sciences, Institute of Biology, Freie Universität Berlin, Königin-Luise-Straße 1-3, 14195, Berlin, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Wurst
mesh_terms: D018533:Biomass; D003583:Cytokinins / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D005838:Genotype; D038821:Mycorrhizae / Q000502:physiology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism*; D018520:Plant Shoots / Q000378:metabolism*; D030821:Plants, Genetically Modified; D013559:Symbiosis / Q000502:physiology*; D014026:Nicotiana / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
chemical_list: D003583:Cytokinins; D010940:Plant Proteins
keywords: Carbon; Cytokinin; Nicotiana tabacum; Phosphate transporter genes; Rhizophagus irregularis; Symbiosis