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Auxin perception is required for arbuscule development in arbuscular mycorrhizal symbiosis
Mohammad Etemadi1, Caroline Gutjahr1, Jean-Malo Couzigou1
1Université Paul Sabatier Toulouse, Unité Mixte de Recherche 5546, Laboratoire de Recherche en Sciences Végétales, F-31326 Castanet-Tolosan cedex, France (M.E., J.-M.C., D.L., G.B., J.-P.C.);Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5546, F-31326 Castanet-Tolosan cedex, France (M.E., J.-M.C., D.L., G.B., J.-P.C.);Institut National Polytechnique-Ecole Nationale Supérieure Agronomique Toulouse, Génomique et Biotechnologie des Fruits, F-31326 Castanet-Tolosan, France (M.E., M.Z., C.A., M.B.);Institut National de la Recherche Agronomique, Génomique et Biotechnologie des Fruits, F-52627 Auzeville, France (M.E., M.Z., C.A., M.B.);Faculty of Biology, Genetics, University of Munich, 82152 Martinsried, Germany (C.G.); andLaboratoire des Interactions Plantes-Microorganismes, Unité Mixte de Recherche 441/2594 Institut National de la Recherche Agronomique-Centre National de la Recherche Scientifique, F-31326 Castanet-Tolosan cedex, France (A.T.).
Abstract:
Most land plant species live in symbiosis with arbuscular mycorrhizal fungi. These fungi differentiate essential functional structures called arbuscules in root cortical cells from which mineral nutrients are released to the plant. We investigated the role of microRNA393 (miR393), an miRNA that targets several auxin receptors, in arbuscular mycorrhizal root colonization. Expression of the precursors of the miR393 was down-regulated during mycorrhization in three different plant species: Solanum lycopersicum, Medicago truncatula, and Oryza sativa. Treatment of S. lycopersicum, M. truncatula, and O. sativa roots with concentrations of synthetic auxin analogs that did not affect root development stimulated mycorrhization, particularly arbuscule formation. DR5-GUS, a reporter for auxin response, was preferentially expressed in root cells containing arbuscules. Finally, overexpression of miR393 in root tissues resulted in down-regulation of auxin receptor genes (transport inhibitor response1 and auxin-related F box) and underdeveloped arbuscules in all three plant species. These results support the conclusion that miR393 is a negative regulator of arbuscule formation by hampering auxin perception in arbuscule-containing cells.
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