A surface-receptor-coupled G protein regulates plant immunity through nuclear protein kinases.

Plants employ cell-surface-localized pattern recognition receptors (PRRs) to recognize immunogenic patterns and activate defenses. How these receptors regulate immune signaling in the nucleus is not well understood. Our previous studies showed that BIK1, a central kinase associated with PRRs, phosphorylates a plant-specific Gα protein called extra-large G protein 2 (XLG2) to positively regulate immunity. Here, we show that this phosphorylation promotes XLG2 nuclear translocation, which is essential for antibacterial immunity. XLG2 interacts with nuclear-localized MUT9-like kinases (MLKs) to regulate transcriptome programming. MLKs negatively regulate plant immunity in a kinase activity-dependent manner, whereas XLG2 promotes defense gene expression and antibacterial immunity likely by inhibiting MLK kinase activity. A C-terminal motif in MLKs is essential for the interaction with XLG2, and this motif is required for the XLG2-mediated defense activation. Together, our findings reveal a previously unknown pathway and mechanisms by which cell surface receptors regulate transcriptome during pathogen invasion.