Surface immune receptors such as flagellin-sensitive 2 (FLS2) are critical for plant defence, and their accumulation at the plasma membrane is tightly controlled by the endomembrane system. Here, we identify the Arabidopsis thaliana prenylated Rab acceptor PRA1.F3 as a positive regulator required for efficient accumulation of FLS2 at the plasma membrane and as a key target of the Shigella type III effector VirA. Although VirA can associate with multiple PRA1 isoforms, immune suppression and enhanced pathogen proliferation in Arabidopsis specifically depend on PRA1.F3. VirA associates with PRA1.F3 at endomembrane compartments and promotes its ubiquitin-proteasome-dependent degradation, leading to reduced FLS2 abundance and attenuation of pattern-triggered immunity. This immune-suppressive activity requires both the GTPase-activating function and membrane association of VirA. In contrast, the closely related isoform PRA1.F4 negatively affects FLS2 accumulation but does not undergo VirA-dependent destabilization. Together, these findings establish PRA1.F3 as a central regulator of immune receptor accumulation and reveal a selective bacterial strategy to subvert host endomembrane regulation and evade immune recognition.
Keywords: FLS2; PRA1 isoforms; Shigella; T3SS; VirA; endomembrane regulation; plant immunity.
© 2026 The Author(s). Plant, Cell & Environment published by John Wiley & Sons Ltd.