title: Pseudomonas fluorescens C7R12 type III secretion system impacts mycorrhization of Medicago truncatula and associated microbial communities.
abstract: Type three secretion systems (T3SSs) mediate cell-to-cell interactions between Gram-negative bacteria and eukaryotes. We hypothesized that fluorescent pseudomonads harboring T3SS (T3SS+) would be beneficial to arbuscular mycorrhizal symbiosis because non-pathogenic fluorescent pseudomonads have been previously shown to be much more abundant in mycorrhizal than in non-mycorrhizal roots. We tested this hypothesis by comparing mycorrhization and the associated rhizosphere microbial communities of Medicago truncatula grown in a non-sterile soil inoculated with either the T3SS+ mycorrhiza helper bacterium Pseudomonas fluorescens (C7R12) or a T3SS- mutant of the strain. Results showed that the bacterial secretion system was responsible for the promotion of mycorrhization because root colonization by arbuscular mycorrhizal fungi was not promoted by the T3SS- mutant. The observed T3SS-mediated promotion of mycorrhization was associated with changes in the rhizosphere bacterial communities and the increased occurrence of Claroidoglomeraceae within the intraradical arbuscular mycorrhizal fungi. Furthermore, both pseudomonad strains promoted the host-free growth of a model arbuscular mycorrhizal fungus in vitro, suggesting that T3SS-mediated promotion of mycorrhization occurs during plant-fungal interactions rather than during the pre-symbiotic phase of fungal growth. Taken together, these data provide evidence for the involvement of T3SS in promoting arbuscular mycorrhization by a model fluorescent pseudomonad and suggest the implication of interactions between the bacterium and mycorrhizas.
authors.affiliation: Agroécologie, AgroSup Dijon, CNRS, INRA, Université Bourgogne Franche-Comté, 21000, Dijon, France.
authors.forename: Amandine
authors.initials: A
authors.lastname: Viollet
authors.affiliation: Agroécologie, AgroSup Dijon, CNRS, INRA, Université Bourgogne Franche-Comté, 21000, Dijon, France.
authors.forename: Barbara
authors.initials: B
authors.lastname: Pivato
authors.affiliation: Agroécologie, AgroSup Dijon, CNRS, INRA, Université Bourgogne Franche-Comté, 21000, Dijon, France.|INRA, UMR1349 IGEPP, 35653, Le Rheu, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Mougel
authors.affiliation: INRA, UMR 113 'Laboratoire des Symbioses Tropicales et Méditerranéennes', Campus International de Baillarguet, TA-A82/J, 34398, Montpellier Cedex 5, France.
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Cleyet-Marel
authors.affiliation: INRA, UMR 113 'Laboratoire des Symbioses Tropicales et Méditerranéennes', Campus International de Baillarguet, TA-A82/J, 34398, Montpellier Cedex 5, France.|Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, AB24 3UU, UK.
authors.forename: Cécile
authors.initials: C
authors.lastname: Gubry-Rangin
authors.affiliation: Agroécologie, AgroSup Dijon, CNRS, INRA, Université Bourgogne Franche-Comté, 21000, Dijon, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Lemanceau
authors.affiliation: Agroécologie, AgroSup Dijon, CNRS, INRA, Université Bourgogne Franche-Comté, 21000, Dijon, France. sylvie.mazurier@dijon.inra.fr.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Mazurier
mesh_terms: D005658:Fungi / Q000145:classification / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D046913:Medicago truncatula / Q000382:microbiology*; D009154:Mutation; D038821:Mycorrhizae / Q000502:physiology*; D018517:Plant Roots / Q000382:microbiology; D011551:Pseudomonas fluorescens / Q000145:classification* / Q000235:genetics / Q000502:physiology*; D012988:Soil Microbiology; D000069296:Type III Secretion Systems / Q000502:physiology*
chemical_list: D000069296:Type III Secretion Systems
keywords: Arbuscular mycorrhiza; Medicago truncatula; Microbial communities; Pseudomonas; Rhizosphere; Type III secretion system