title: Symbiotic Fungi Control Plant Root Cortex Development through the Novel GRAS Transcription Factor MIG1.
abstract: In an approaching scenario of soil nutrient depletion, root association with soil microorganisms can be key for plant health and sustainability [1-3]. Symbiotic arbuscular mycorrhizal (AM) fungi are major players in helping plants growing under nutrient starvation conditions. They provide plants with minerals like phosphate and, furthermore, act as modulators of plant growth altering the root developmental program [4, 5]. However, the precise mechanisms involved in this latter process are not well understood. Here, we show that AM fungi are able to modulate root cortex development in Medicago truncatula by activating a novel GRAS-domain transcription factor, MIG1, that determines the size of cortical root cells. MIG1 expression peaks in arbuscule-containing cells, suggesting a role in cell remodeling during fungal accommodation. Roots ectopically expressing MIG1 become thicker due to an increase in the number and width of cortical cells. This phenotype is fully counteracted by gibberellin (GA) and phenocopied with a GA biosynthesis inhibitor or by expression of a dominant DELLA (Δ18DELLA1) protein. MIG1 downregulation leads to malformed arbuscules, a phenotype rescued by Δ18DELLA1, suggesting that MIG1 intersects with the GA signaling to control cell morphogenesis through DELLA1. DELLA1 was shown to be a central node controlling arbuscule branching [6-8]. Now we provide evidence that, together with MIG1, DELLA1 is responsible for radial cortical cell expansion during arbuscule development. Our data point toward DELLA proteins being not only longitudinal root growth repressors [9] but also positive regulators of cortical radial cell expansion, extending the knowledge of how DELLAs control root growth.
authors.affiliation: Molecular Phytopathology, Botanical Institute, Karlsruhe Institute of Technology (KIT), Fritz Haber-Weg 4, 76131 Karlsruhe, Germany.
authors.forename: Carolin
authors.initials: C
authors.lastname: Heck
authors.affiliation: Molecular Phytopathology, Botanical Institute, Karlsruhe Institute of Technology (KIT), Fritz Haber-Weg 4, 76131 Karlsruhe, Germany.
authors.forename: Hannah
authors.initials: H
authors.lastname: Kuhn
authors.affiliation: Molecular Phytopathology, Botanical Institute, Karlsruhe Institute of Technology (KIT), Fritz Haber-Weg 4, 76131 Karlsruhe, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Heidt
authors.affiliation: Molecular Phytopathology, Botanical Institute, Karlsruhe Institute of Technology (KIT), Fritz Haber-Weg 4, 76131 Karlsruhe, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Walter
authors.affiliation: Molecular Phytopathology, Botanical Institute, Karlsruhe Institute of Technology (KIT), Fritz Haber-Weg 4, 76131 Karlsruhe, Germany.
authors.forename: Nina
authors.initials: N
authors.lastname: Rieger
authors.affiliation: Molecular Phytopathology, Botanical Institute, Karlsruhe Institute of Technology (KIT), Fritz Haber-Weg 4, 76131 Karlsruhe, Germany. Electronic address: natalia.requena@kit.edu.
authors.forename: Natalia
authors.initials: N
authors.lastname: Requena
mesh_terms: D018506:Gene Expression Regulation, Plant; D046913:Medicago truncatula / Q000235:genetics* / Q000254:growth & development* / Q000382:microbiology; D038821:Mycorrhizae / Q000502:physiology*; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development / Q000382:microbiology; D013559:Symbiosis; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D014157:Transcription Factors