Biomolecular condensates of ATG18 reshape ER to promote autophagy in plants

Here, we demonstrate that Arabidopsis ATG18a, a key organizer of early autophagosome formation, undergoes phase separation to form biomolecular condensates on the ER membrane, which progress from highly mobile droplets to stable ring-like structures, while the ER is reshaped.

We discovered that ATG18a condensates work together with RHD3, an ER membrane-shaping protein, with RABC1 serving as a molecular linker between them. Importantly, RABC1 facilitates both RHD3 assembly necessary for formation of ringlike ER structures and its interaction with ATG18a condensates. These findings reveal a novel mechanism whereby biomolecular condensates, work together with membrane shaping proteins to reshape specialized membrane domains through wetting interactions, providing fundamental insights into autophagosome formation in plant stress responses.