title: Phosphate systemically inhibits development of arbuscular mycorrhiza in Petunia hybrida and represses genes involved in mycorrhizal functioning.
abstract: Most terrestrial plants form arbuscular mycorrhiza (AM), mutualistic associations with soil fungi of the order Glomeromycota. The obligate biotrophic fungi trade mineral nutrients, mainly phosphate (P(i) ), for carbohydrates from the plants. Under conditions of high exogenous phosphate supply, when the plant can meet its own P requirements without the fungus, AM are suppressed, an effect which could be interpreted as an active strategy of the plant to limit carbohydrate consumption of the fungus by inhibiting its proliferation in the roots. However, the mechanisms involved in fungal inhibition are poorly understood. Here, we employ a transcriptomic approach to get insight into potential shifts in metabolic activity and symbiotic signalling, and in the defence status of plants exposed to high P(i) levels. We show that in mycorrhizal roots of petunia, a similar set of symbiosis-related genes is expressed as in mycorrhizal roots of Medicago, Lotus and rice. P(i) acts systemically to repress symbiotic gene expression and AM colonization in the root. In established mycorrhizal roots, P(i) repressed symbiotic gene expression rapidly, whereas the inhibition of colonization followed with a lag of more than a week. Taken together, these results suggest that P(i) acts by repressing essential symbiotic genes, in particular genes encoding enzymes of carotenoid and strigolactone biosynthesis, and symbiosis-associated phosphate transporters. The role of these effects in the suppression of symbiosis under high P(i) conditions is discussed.
authors.affiliation: Department of Biology, University of Fribourg, Rte Albert Gockel 3, CH-1700 Fribourg, Switzerland.
authors.forename: Florence
authors.initials: F
authors.lastname: Breuillin
authors.forename: Jonathan
authors.initials: J
authors.lastname: Schramm
authors.forename: Mohammad
authors.initials: M
authors.lastname: Hajirezaei
authors.forename: Amir
authors.initials: A
authors.lastname: Ahkami
authors.forename: Patrick
authors.initials: P
authors.lastname: Favre
authors.forename: Uwe
authors.initials: U
authors.lastname: Druege
authors.forename: Bettina
authors.initials: B
authors.lastname: Hause
authors.forename: Marcel
authors.initials: M
authors.lastname: Bucher
authors.forename: Tobias
authors.initials: T
authors.lastname: Kretzschmar
authors.forename: Eligio
authors.initials: E
authors.lastname: Bossolini
authors.forename: Cris
authors.initials: C
authors.lastname: Kuhlemeier
authors.forename: Enrico
authors.initials: E
authors.lastname: Martinoia
authors.forename: Philipp
authors.initials: P
authors.lastname: Franken
authors.forename: Uwe
authors.initials: U
authors.lastname: Scholz
authors.forename: Didier
authors.initials: D
authors.lastname: Reinhardt
mesh_terms: D020224:Expressed Sequence Tags; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D015723:Gene Library; D038821:Mycorrhizae / Q000502:physiology*; D020411:Oligonucleotide Array Sequence Analysis; D032306:Petunia / Q000235:genetics / Q000382:microbiology* / Q000502:physiology; D010710:Phosphates / Q000494:pharmacology*; D018517:Plant Roots / Q000235:genetics* / Q000382:microbiology / Q000502:physiology; D013559:Symbiosis; D014158:Transcription, Genetic
chemical_list: D010710:Phosphates