title: Remodeling of the infection chamber before infection thread formation reveals a two-step mechanism for rhizobial entry into the host legume root hair.
abstract: In many legumes, root entry of symbiotic nitrogen-fixing rhizobia occurs via host-constructed tubular tip-growing structures known as infection threads (ITs). Here, we have used a confocal microscopy live-tissue imaging approach to investigate early stages of IT formation in Medicago truncatula root hairs (RHs) expressing fluorescent protein fusion reporters. This has revealed that ITs only initiate 10 to 20 h after the completion of RH curling, by which time major modifications have occurred within the so-called infection chamber, the site of bacterial entrapment. These include the accumulation of exocytosis (M. truncatula Vesicle-Associated Membrane Protein721e)- and cell wall (M. truncatula EARLY NODULIN11)-associated markers, concomitant with radial expansion of the chamber. Significantly, the infection-defective M. truncatula nodule inception-1 mutant is unable to create a functional infection chamber. This underlines the importance of the NIN-dependent phase of host cell wall remodeling that accompanies bacterial proliferation and precedes IT formation, and leads us to propose a two-step model for rhizobial infection initiation in legume RHs.
authors: Laboratoire des Interactions Plantes Micro-organismes, Institut National de la Recherche Agronomique (Unité Mixte de Recherche 441), Centre National de la Recherche Scientifique (Unité Mixte de Recherche 2594), F-31320 Castanet-Tolosan, France (J.F., A.T., M.C., F.d.C.-N., D.G.B.);Plant Science, Laboratory of Molecular Biology, Wageningen University, 6708PB Wageningen, The Netherlands (S.I., E.L.); andDipartimento di Scienze della Vita e Biologia dei Sistemi, Università di Torino, 10125 Torino, Italy (A.G.) joelle.fournier@toulouse.inra.fr.
authors: Joëlle
authors: http://orcid.org/0000-0003-3746-8080
authors: J
authors: Fournier
authors: Laboratoire des Interactions Plantes Micro-organismes, Institut National de la Recherche Agronomique (Unité Mixte de Recherche 441), Centre National de la Recherche Scientifique (Unité Mixte de Recherche 2594), F-31320 Castanet-Tolosan, France (J.F., A.T., M.C., F.d.C.-N., D.G.B.);Plant Science, Laboratory of Molecular Biology, Wageningen University, 6708PB Wageningen, The Netherlands (S.I., E.L.); andDipartimento di Scienze della Vita e Biologia dei Sistemi, Università di Torino, 10125 Torino, Italy (A.G.).
authors: Alice
authors: A
authors: Teillet
authors: Laboratoire des Interactions Plantes Micro-organismes, Institut National de la Recherche Agronomique (Unité Mixte de Recherche 441), Centre National de la Recherche Scientifique (Unité Mixte de Recherche 2594), F-31320 Castanet-Tolosan, France (J.F., A.T., M.C., F.d.C.-N., D.G.B.);Plant Science, Laboratory of Molecular Biology, Wageningen University, 6708PB Wageningen, The Netherlands (S.I., E.L.); andDipartimento di Scienze della Vita e Biologia dei Sistemi, Università di Torino, 10125 Torino, Italy (A.G.).
authors: Mireille
authors: M
authors: Chabaud
authors: Laboratoire des Interactions Plantes Micro-organismes, Institut National de la Recherche Agronomique (Unité Mixte de Recherche 441), Centre National de la Recherche Scientifique (Unité Mixte de Recherche 2594), F-31320 Castanet-Tolosan, France (J.F., A.T., M.C., F.d.C.-N., D.G.B.);Plant Science, Laboratory of Molecular Biology, Wageningen University, 6708PB Wageningen, The Netherlands (S.I., E.L.); andDipartimento di Scienze della Vita e Biologia dei Sistemi, Università di Torino, 10125 Torino, Italy (A.G.).
authors: Sergey
authors: S
authors: Ivanov
authors: Laboratoire des Interactions Plantes Micro-organismes, Institut National de la Recherche Agronomique (Unité Mixte de Recherche 441), Centre National de la Recherche Scientifique (Unité Mixte de Recherche 2594), F-31320 Castanet-Tolosan, France (J.F., A.T., M.C., F.d.C.-N., D.G.B.);Plant Science, Laboratory of Molecular Biology, Wageningen University, 6708PB Wageningen, The Netherlands (S.I., E.L.); andDipartimento di Scienze della Vita e Biologia dei Sistemi, Università di Torino, 10125 Torino, Italy (A.G.).
authors: Andrea
authors: A
authors: Genre
authors: Laboratoire des Interactions Plantes Micro-organismes, Institut National de la Recherche Agronomique (Unité Mixte de Recherche 441), Centre National de la Recherche Scientifique (Unité Mixte de Recherche 2594), F-31320 Castanet-Tolosan, France (J.F., A.T., M.C., F.d.C.-N., D.G.B.);Plant Science, Laboratory of Molecular Biology, Wageningen University, 6708PB Wageningen, The Netherlands (S.I., E.L.); andDipartimento di Scienze della Vita e Biologia dei Sistemi, Università di Torino, 10125 Torino, Italy (A.G.).
authors: Erik
authors: E
authors: Limpens
authors: Laboratoire des Interactions Plantes Micro-organismes, Institut National de la Recherche Agronomique (Unité Mixte de Recherche 441), Centre National de la Recherche Scientifique (Unité Mixte de Recherche 2594), F-31320 Castanet-Tolosan, France (J.F., A.T., M.C., F.d.C.-N., D.G.B.);Plant Science, Laboratory of Molecular Biology, Wageningen University, 6708PB Wageningen, The Netherlands (S.I., E.L.); andDipartimento di Scienze della Vita e Biologia dei Sistemi, Università di Torino, 10125 Torino, Italy (A.G.).
authors: Fernanda
authors: F
authors: de Carvalho-Niebel
authors: Laboratoire des Interactions Plantes Micro-organismes, Institut National de la Recherche Agronomique (Unité Mixte de Recherche 441), Centre National de la Recherche Scientifique (Unité Mixte de Recherche 2594), F-31320 Castanet-Tolosan, France (J.F., A.T., M.C., F.d.C.-N., D.G.B.);Plant Science, Laboratory of Molecular Biology, Wageningen University, 6708PB Wageningen, The Netherlands (S.I., E.L.); andDipartimento di Scienze della Vita e Biologia dei Sistemi, Università di Torino, 10125 Torino, Italy (A.G.).
authors: David G
authors: DG
authors: Barker
mesh_terms: D015415:Biomarkers; D002473:Cell Wall / Q000378:metabolism; D017930:Genes, Reporter; D046913:Medicago truncatula / Q000166:cytology / Q000235:genetics / Q000382:microbiology* / Q000502:physiology; D008954:Models, Biological; D009154:Mutation; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000166:cytology / Q000235:genetics / Q000382:microbiology* / Q000502:physiology; D016962:Sinorhizobium meliloti / Q000502:physiology*; D013559:Symbiosis
chemical_list: D015415:Biomarkers; D010940:Plant Proteins