Role of G3BP1 Phosphorylation in the Regulation of Plant Immunity in Arabidopsis Thaliana

A central regulator of condensate formation in mammals is the Ras GTPase-activating protein SH3 domain-binding protein (G3BP) family of RNA-binding proteins. In Arabidopsis, G3BP homologs can also form condensates and exhibit diverse expression patterns and subcellular localization. Previously, we identified G3BP1 as a negative regulator of plant immunity that is phosphorylated at Ser257 in vivo. Here, we generated phospho-mimic (G3BP1D) and phospho-dead (G3BP1A) variants and expressed them in Arabidopsis, revealing that the phosphorylation state of G3BP1 affects susceptibility to bacterial infection by influencing ROS production and salicylic acid (SA) accumulation. G3BP1 phosphorylation also influences stomatal immunity by maintaining stomatal opening, thereby modulating pre-invasive defense mechanisms. Furthermore, we show that phosphorylation at Ser257 contributes to the stabilization of G3BP1 by limiting its degradation. Collectively, these findings identify G3BP1 phosphorylation as an important regulatory mechanism in plant immunity and provide new insights into the role of RNA-binding proteins in plant defense responses.