Molecular condensation on plasma membrane during plant-pathogen interactions

Abstract

Phytobacteria compromise plant cells by releasing intrinsically disordered type III effector (T3E) proteins over time to undermine host defense and development. Yet, apart from the cytoplasmic T3Es-triggered immunity, we have limited knowledge about host invasion by many membrane-bound T3Es. This study investigates the molecular interplays between the Xanthomonas campestris pv. campestris T3E XopR and its targeted plant plasma membrane (PM). XopR subverts the host via a dose-dependent percolation progression on the PM, involving local clustering, network spanning, and ultimately, density redistribution causing PM deformation. Distinct from conventional phase growth and coalescence post-nucleation, the expanding network on a 2D surface commandeers the PM, disrupting PM-dependent host functions. Plants counteract by utilizing mechanoregulation, employing their PM-actin cytoskeleton continuum to control XopR's phase progression and host subversion. Our study illuminates the dynamic interplay between bacterial T3E's percolation and phase separation, and the mechanical regulation in plants during host-pathogen interactions. And further studies identified a key plasma membrane localized regulatory protein RIN4, which is targeted by a bunch of effector proteins and guarded by 2 coiled-coil nucleotide-binding leucine-rich repeat receptors (CNL) receptors, as an interacting partner of XopR. We demonstrated that RIN4 protein could form biomolecular condensates in vivo and in vitro, the biophysical of property of which can be altered by XopR, resulting in suppressed phosphorylation ratio of RIN4. The physiological consequence of RIN4 proteins with compromised phosphorylation availability leads to vitiated resistance to pathogen infection. Taken together, our work unveiled possible new ways of effector protein progression on the plasma membrane, and how changes in molecular condensations could impair functional output.