ER-driven Contact Sites in Autophagosome Biogenesis Sequence

Autophagosome biogenesis is a highly coordinated membrane remodeling process that relies on the de novo formation and expansion of the phagophore, yet the cellular principles governing its spatial and temporal organization remain incompletely understood. Accumulating evidence now places the endoplasmic reticulum (ER) at the center of this process, not merely as a membrane source, but as a dynamic scaffold that organizes phagophore assembly through extensive membrane contact sites with multiple organelles. ER-mediated contacts with endosomes, mitochondria, the plasma membrane, and ER-Golgi intermediates create specialized microenvironments that integrate signaling, lipid transfer, vesicle formation and trafficking, and biophysical constraints to drive phagophore nucleation and growth. These contact sites enable the coordinated mobilization of diverse membrane carriers and autophagy regulators in a stress- and context-dependent manner. In this review, we discuss how ER-driven membrane contact sites orchestrate autophagosome biogenesis, highlight emerging mechanistic and biophysical concepts, and consider their broader implications for cellular stress adaptation and disease.