Biomolecular condensates of ATG18 reshape ER to promote autophagy in plants

Autophagosomes originate from and maintain association with the endoplasmic
reticulum (ER) during their formation, yet how these processes are molecularly
coordinated in plants remains poorly understood. 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.

Here all original and full western blots are included.