Abstract:
Plants face a wide range of biotic and abiotic stresses that threaten their growth, productivity, and survival. To respond effectively, plants employ multilayered immune signaling networks and cellular adaptation mechanisms, including transcriptional reprogramming and the formation of biomolecular condensates such as stress granules (SGs). This study investigates the multifunctional role of the RNA-binding protein AtG3BP1 (Ras-GTPase-activating protein SH3-domain-binding protein 1) in coordinating plant immune responses and stress adaptation in Arabidopsis thaliana. Using phosphoproteomics and in vitro kinase assays, we identify AtG3BP1 as a direct substrate of mitogen-activated protein kinases (MPK3, MPK4, and MPK6). Functional analysis of phospho-dead and phospho-mimic AtG3BP1 variants reveals that phosphorylation at Ser-257 modulates plant susceptibility to Pseudomonas syringae, affects stomatal immunity, and regulates the production of reactive oxygen species (ROS) and salicylic acid (SA). In parallel, we explore the role of AtG3BP1 in SG dynamics under heat and drought stress. Through proteomic and transcriptomic profiling of SG-enriched fractions, we show that AtG3BP1 contributes to the selective recruitment of stress-responsive mRNAs and protein interactors. Despite AtG3BP1 not being essential for SG formation, its phosphorylation influences protein stability and post-transcriptional regulation during stress. Together, our findings reveal AtG3BP1 as a MAPK-regulated hub that integrates immune signaling with stress granule-mediated RNA metabolism, offering novel insights into the post-translational and post-transcriptional control of plant stress responses.