title: Arbuscular mycorrhizal symbiosis is accompanied by local and systemic alterations in gene expression and an increase in disease resistance in the shoots.
abstract: In natural ecosystems, the roots of many plants exist in association with arbuscular mycorrhizal (AM) fungi, and the resulting symbiosis has profound effects on the plant. The most frequently documented response is an increase in phosphorus nutrition; however, other effects have been noted, including increased resistance to abiotic and biotic stresses. Here we used a 16,000-feature oligonucleotide array and real-time quantitative RT-PCR to explore transcriptional changes triggered in Medicago truncatula roots and shoots as a result of AM symbiosis. By controlling the experimental conditions, phosphorus-related effects were minimized, and both local and systemic transcriptional responses to the AM fungus were revealed. The transcriptional response of the roots and shoots differed in both the magnitude of gene induction and the predicted functional categories of the mycorrhiza-regulated genes. In the roots, genes regulated in response to three different AM fungi were identified, and, through split-root experiments, an additional layer of regulation, in the colonized or non-colonized sections of the mycorrhizal root system, was uncovered. Transcript profiles of the shoots of mycorrhizal plants indicated the systemic induction of many genes predicted to be involved in stress or defense responses, and suggested that mycorrhizal plants might display enhanced disease resistance. Experimental evidence supports this prediction, and mycorrhizal M. truncatula plants showed increased resistance to a virulent bacterial pathogen, Xanthomonas campestris. Thus, the symbiosis is accompanied by a complex pattern of local and systemic changes in gene expression, including the induction of a functional defense response.
authors.affiliation: Boyce Thompson Institute for Plant Research, Cornell University, Tower Road, Ithaca, NY14853, USA.
authors.forename: Jinyuan
authors.initials: J
authors.lastname: Liu
authors.forename: Ignacio
authors.initials: I
authors.lastname: Maldonado-Mendoza
authors.forename: Melina
authors.initials: M
authors.lastname: Lopez-Meyer
authors.forename: Foo
authors.initials: F
authors.lastname: Cheung
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Town
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Harrison
mesh_terms: D018506:Gene Expression Regulation, Plant; D007113:Immunity, Innate; D046913:Medicago truncatula / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D038821:Mycorrhizae / Q000378:metabolism*; D010935:Plant Diseases / Q000235:genetics / Q000276:immunology* / Q000382:microbiology*; D018517:Plant Roots / Q000378:metabolism / Q000382:microbiology; D018520:Plant Shoots / Q000235:genetics / Q000276:immunology* / Q000382:microbiology; D013559:Symbiosis / Q000502:physiology*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D016959:Xanthomonas campestris / Q000502:physiology