G3BP1 Phosphorylation Regulates Plant Immunity in Arabidopsis

Mitogen-activated protein kinase (MAPK) cascades play critical roles in plant immunity by phosphorylating downstream effectors that regulate stress responses. While MAPK-mediated transcriptional regulation has been well examined, the involvement of MAPKs in post-transcriptional and post-translational regulation is still poorly understood. In this study, we identify the RNA binding-protein AtG3BP1 as a phosphorylation target of MPK3, MPK4, and MPK6 and demonstrate that phosphorylation of AtG3BP1 at Ser257 modulates key aspects of Arabidopsis immunity. Using phospho-mimic (G3BP1D) and phospho-dead (G3BP1A) mutants, we investigated the functional consequences of AtG3BP1 phosphorylation. Our data indicate that phosphorylation of AtG3BP1 promotes susceptibility to bacterial infection, suppresses accumulation of reactive oxygen species (ROS), and downregulates salicylic acid (SA) biosynthesis. Furthermore, we demonstrate that AtG3BP1 phosphorylation influences stomatal immunity by maintaining stomatal opening, thereby regulating pre-invasive defense mechanisms. Additionally, we provide evidence that phosphorylation stabilizes AtG3BP1 and prevents its degradation via the proteasome, thus leading to sustained immune signaling. These findings validate AtG3BP1 as a central integrator of MAPK signaling during plant immunity and reveal a new level of post-translational control. This study enhances our understanding of plant defense mechanisms and provides potential targets for engineering disease-resistant crops.