title: MtbHLH1, a bHLH transcription factor involved in Medicago truncatula nodule vascular patterning and nodule to plant metabolic exchanges.
abstract: This study aimed at defining the role of a basic helix-loop-helix (bHLH) transcription factor gene from Medicago truncatula, MtbHLH1, whose expression is upregulated during the development of root nodules produced upon infection by rhizobia bacteria. We used MtbHLH1 promoter::GUS fusions and quantitative reverse-transcription polymerase chain reaction analyses to finely characterize the MtbHLH1 expression pattern. We altered MtbHLH1 function by expressing a dominantly repressed construct (CRES-T approach) and looked for possible MtbHLH1 target genes by transcriptomics. We found that MtbHLH1 is expressed in nodule primordia cells derived from pericycle divisions, in nodule vascular bundles (VBs) and in uninfected cells of the nitrogen (N) fixation zone. MtbHLH1 is also expressed in root tips, lateral root primordia cells and root VBs, and induced upon auxin treatment. Altering MtbHLH1 function led to an unusual phenotype, with a modified patterning of nodule VB development and a reduced growth of aerial parts of the plant, even though the nodules were able to fix atmospheric N. Several putative MtbHLH1 regulated genes were identified, including an asparagine synthase and a LOB (lateral organ boundary) transcription factor. Our results suggest that the MtbHLH1 gene is involved in the control of nodule vasculature patterning and nutrient exchanges between nodules and roots.
authors.affiliation: Laboratoire des Interactions Plantes Microorganismes, Unité Mixte de Recherche, Institut National de la Recherche Agronomique - Centre National de la Recherche Scientifique 441/2594, F-31320 Castanet Tolosan, France.
authors.forename: Laurence
authors.initials: L
authors.lastname: Godiard
authors.affiliation: Laboratoire des Interactions Plantes Microorganismes, Unité Mixte de Recherche, Institut National de la Recherche Agronomique - Centre National de la Recherche Scientifique 441/2594, F-31320 Castanet Tolosan, France.
authors.forename: Agnès
authors.initials: A
authors.lastname: Lepage
authors.affiliation: Laboratoire des Interactions Plantes Microorganismes, Unité Mixte de Recherche, Institut National de la Recherche Agronomique - Centre National de la Recherche Scientifique 441/2594, F-31320 Castanet Tolosan, France.
authors.forename: Sandra
authors.initials: S
authors.lastname: Moreau
authors.affiliation: Jian-Qiu Wu's laboratory, Ohio State University, 612 Biosciences Building, 484 W 12th Ave, Columbus, OH 43210, USA.
authors.forename: Damien
authors.initials: D
authors.lastname: Laporte
authors.affiliation: Laboratoire des Interactions Plantes Microorganismes, Unité Mixte de Recherche, Institut National de la Recherche Agronomique - Centre National de la Recherche Scientifique 441/2594, F-31320 Castanet Tolosan, France.
authors.forename: Marion
authors.initials: M
authors.lastname: Verdenaud
authors.affiliation: Laboratoire des Interactions Plantes Microorganismes, Unité Mixte de Recherche, Institut National de la Recherche Agronomique - Centre National de la Recherche Scientifique 441/2594, F-31320 Castanet Tolosan, France.
authors.forename: Ton
authors.initials: T
authors.lastname: Timmers
authors.affiliation: Laboratoire des Interactions Plantes Microorganismes, Unité Mixte de Recherche, Institut National de la Recherche Agronomique - Centre National de la Recherche Scientifique 441/2594, F-31320 Castanet Tolosan, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Gamas
mesh_terms: D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D019521:Body Patterning; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D007210:Indoleacetic Acids / Q000494:pharmacology; D046913:Medicago truncatula / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology / Q000502:physiology; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000235:genetics; D010641:Phenotype; D010937:Plant Growth Regulators / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D055170:Plant Root Nodulation; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D012231:Rhizobium / Q000235:genetics / Q000502:physiology*; D053204:Root Nodules, Plant / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D013559:Symbiosis / Q000235:genetics
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D010940:Plant Proteins