Skip to main content
ISMPMI Congress 2025 Main banner
Icon Legend
This session is not in your schedule.
This session is in your schedule. Click again to remove it.

Concurrent Session

Session: Concurrent Session: Microbial infection strategies (pathogens & non-pathogens)

Identification of the key virulence factor of the atypical rhizobia that trigger pathogenicity and nodulation on the same host

Monday, July 14, 2025
16:00 - 16:15  
Location: Confex Hall 1+2

    Author(s)

  • TF

    Tifaine Folletti

    Laboratoire des Interactions Plantes-Microbes-Environnement (LIPME), Université de Toulouse, INRAE, CNRS
    Castanet Tolosan, Midi-Pyrenees, France

  • SM

    Sophie Massot

    Université Paris Cité, CNRS, INRAE, Institute of Plant Sciences Paris-Saclay, 91190 Gif sur Yvette, France
    Gif sur Yvette, Ile-de-France, France

  • LS

    Laurent Sauviac

    Laboratoire des Interactions Plantes-Microbes-Environnement (LIPME), Université de Toulouse, INRAE, CNRS
    Castanet Tolosan, Midi-Pyrenees, France

  • FV

    Fabienne Vailleau

    Director
    Laboratoire des Interactions Plantes-Microbes-Environnement (LIPME), Université de Toulouse, INRAE, CNRS
    Castanet Tolosan, Midi-Pyrenees, France

  • JP

    Jörn Piel

    Institute of Microbiology, Eidgenössische Technische Hochschule Zurich
    Zurich, Zurich, Switzerland

  • PR

    Pascal Ratet

    Université Paris-Saclay, CNRS, INRAE, Université Evry, Institute of Plant Sciences Paris-Saclay
    Gif sur Yvette, Ile-de-France, France

    • Presenting Author(s)

  • BG

    Benjamin Gourion

    Laboratoire des Interactions Plantes-Microbes-Environnement (LIPME), Université de Toulouse, INRAE, CNRS
    Castanet Tolosan, Midi-Pyrenees, France

Abstract Text:

The frontiers between pathogenic and mutualistic organisms are sometimes blurry. We have recently characterized a clade of atypical rhizobia that trigger plant death on young seedlings and nodulation on older plants of the same species. The virulence factors involved in the pathogenic interactions were not known. To identify them, we exploited the diversity of the Ensifer adhaerens species and looked for specificities shared by pathogenic strains and absent in non-pathogenic ones. We thus performed comparative genomics that led us to investigate the role of a 200kbp plasmid harboring 34% of CDS specific to the pathogenic strains. We identified on this plasmid a 70kb region that includes a biosynthetic gene cluster (BGC) that likely encodes for polyketide synthases. Computational biology predicted that the BGC might be responsible for the production of spliceostatin, a toxin that inhibits the spliceosome. We constructed mutants deleted for this BGC in the T4 strain, the model bacterium of this clade. Plant inoculations revealed that the deletion mutant was totally avirulent suggesting that this BGC is crucial for virulence. We then confirmed the role of this BGC by constructing a deletion mutant that displayed the same avirulent phenotype in T173, another strain of this clade. Together our data indicate that the spliceostatin BGC is the key factor of pathogenicity in this atypical clade of rhizobia, triggering nodulation on developed plant and plant death on young seedlings.