A phase-separated nuclear GBPL circuit controls immunity in plants

Liquid-liquid phase separation (LLPS) has emerged as a central paradigm for understanding how membrane-less organelles compartmentalize diverse cellular activities in eukaryotes. Here, we identified a new superfamily of plant Guanylate-Binding Protein-Like GTPases (GBPLs) that assemble LLPS-driven condensates within the nucleus to protect against infection and autoimmunity. In Arabidopsis thaliana, two family members - GBPL1 and GBPL3 - undergo phase transition behavior to control transcriptional responses as part of an allosteric switch triggered by exposure to biotic stress. GBPL1, a pseudoGTPase, sequesters catalytically-active GBPL3 under basal conditions but is displaced by GBPL3 LLPS when it enters the nucleus following immune cues to drive formation of unique membrane-less organelles termed GDACs (GBPL Defense-Activated Condensates) that we visualized by in situ cryo-electron tomography. Within these mesoscale GDAC structures, native GBPL3 directly bound defense gene promoters an...