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Poster

Session: Session 1 Presenting Authors at Posters (Evens)

P-092 - The Pseudomonas syringae effector AvrE1 induces CAR1-mediated stomatal immunity in Arabidopsis and prevents pathogen invasion

Tuesday, July 15, 2025
09:55 - 11:30  
Location: Confex Hall 3
Extracellular & Intracellular non-self recognition & signaling

    Presenting Author(s)

  • TA

    Tamar V. Av-Shalom (she/her/hers)

    PhD Candidate
    Department of Cell and Systems Biology, University of Toronto
    Toronto, Ontario, Canada

    • Author(s)

  • RS

    Racquel A. Singh (she/her/hers)

    PhD Candidate
    Department of Cell and Systems Biology, University of Toronto
    Toronto, Ontario, Canada

  • RG

    Reid Gohmann

    Ohio State University
    Columbus, Ohio, United States

  • DM

    David Mackey

    Professor
    Ohio State University
    Columbus, Ohio, United States

  • DD

    Darrell Desveaux

    Professor
    Department of cell and Systems Biology, University of Toronto
    Toronto, Ontario, Canada

  • DG

    David S. Guttman

    Professor
    Department of Cell and Systems Biology, University of Toronto
    Toronto, Ontario, Canada

The bacterial phytopathogen, Pseudomonas syringae, begins its disease cycle when it invades the apoplastic space in the leaf by entering through natural openings such as stomata. A general, pre-invasive, host defence response triggered by conserved microbe associated molecular patterns (MAMPs) is to restrict pathogen access to the leaf apoplast by closing stomata. Successful P. syringae strains reopen stomata using phytotoxins and effectors, facilitating colonization of the apoplastic space. In this study we show that stomatal reopening is inhibited by the recognition of the conserved P. syringae type III effector AvrE1 by the Arabidopsis resistance protein CAR1; a nucleotide-binding leucine-rich repeat (NLR) protein that is expressed 10-fold higher in guard cells compared to mesophyll tissues. We show that CAR1 triggers a stomatal immune response that reinforces and extends MAMP induced stomatal closure, further preventing pathogen invasion. We also show that the CAR1 immune response suppresses virulence when the pathogen must invade the leaf tissue after surface inoculation but does not provide any protection when strains are directly injected into the tissue, which bypasses stomatal immunity. As such, the pre-invasive immune response provided by CAR1 against this conserved effector represents a significant barrier to early colonization of this microbe in the leaf tissue. Our work describes the first tissue specific effector-triggered immune response in plants.