TORC1-dependent sorting of PI(3,5)P ₂ is required for vacuole membrane remodeling and signaling endosome formation

Lysosomes, as central organelles of the endolysosomal system, support cell growth by releasing nutrients derived from hydrolytic digestion of macromolecules. Additionally, they serve as storage organelles for ions and amino acids and must respond to changes in osmolarity by adjusting their membrane to maintain membrane integrity. The nutrient-sensing target of rapamycin complex 1 (TORC1) and the lipid kinase Fab1 (PIKfyve in mammals) are key regulators of these processes on yeast vacuoles. TORC1 phosphorylates Fab1, yet how their activities are functionally coupled is unknown. Here, we show that yeast TORC1 is essential for the sorting of Fab1-derived phosphatidylinositol-3,5-bisphosphate (PI(3,5)P₂) from vacuoles to signaling endosomes (SEs), whose formation depends on the CROP membrane remodeling complex. TORC1 phosphorylation activates Fab1, presumably to maintain elevated PI(3,5)P₂ levels on SEs toward cell growth. In mutants defective in endosome-vacuole fusion, PI(3,5)P₂ accumulates on endosomes adjacent to the vacuole, indicating that its hydrolysis primarily occurs on the vacuolar membrane. Our findings reveal that synthesis and spatial distribution of the vacuolar signaling lipid PI(3,5)P₂ are directly coordinated by TORC1, coupling nutrient sensing to membrane remodeling and endosomal signaling.