title: The RPG gene of Medicago truncatula controls Rhizobium-directed polar growth during infection.
abstract: Rhizobia can infect roots of host legume plants and induce new organs called nodules, in which they fix atmospheric nitrogen. Infection generally starts with root hair curling, then proceeds inside newly formed, intracellular tubular structures called infection threads. A successful symbiotic interaction relies on infection threads advancing rapidly at their tips by polar growth through successive cell layers of the root toward developing nodule primordia. To identify a plant component that controls this tip growth process, we characterized a symbiotic mutant of Medicago truncatula, called rpg for rhizobium-directed polar growth. In this mutant, nitrogen-fixing nodules were rarely formed due to abnormally thick and slowly progressing infection threads. Root hair curling was also abnormal, indicating that the RPG gene fulfils an essential function in the process whereby rhizobia manage to dominate the process of induced tip growth for root hair infection. Map-based cloning of RPG revealed a member of a previously unknown plant-specific gene family encoding putative long coiled-coil proteins we have called RRPs (RPG-related proteins) and characterized by an "RRP domain" specific to this family. RPG expression was strongly associated with rhizobial infection, and the RPG protein showed a nuclear localization, indicating that this symbiotic gene constitutes an important component of symbiotic signaling.
authors.affiliation: Laboratoire des Interactions Plantes-Microorganismes, Unité Mixte de Recherche 441/2594 L'Institut National de la Recherche Agronomique/Centre National de la Recherche Scientifique, F-31326 Castanet-Tolosan, France.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Arrighi
authors.forename: Olivier
authors.initials: O
authors.lastname: Godfroy
authors.forename: Françoise
authors.initials: F
authors.lastname: de Billy
authors.forename: Olivier
authors.initials: O
authors.lastname: Saurat
authors.forename: Alain
authors.initials: A
authors.lastname: Jauneau
authors.forename: Clare
authors.initials: C
authors.lastname: Gough
mesh_terms: D001483:Base Sequence; D017343:Genes, Plant / Q000235:genetics / Q000502:physiology*; D046913:Medicago truncatula / Q000235:genetics* / Q000382:microbiology; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D010940:Plant Proteins / Q000235:genetics / Q000502:physiology; D018517:Plant Roots / Q000254:growth & development / Q000382:microbiology; D012231:Rhizobium; D013559:Symbiosis
chemical_list: D009687:Nuclear Proteins; D010940:Plant Proteins