Figures Autophagy

Autophagy-deficient fission yeast cells display mating defects and are unable to recover from amino acid starvation, even when external amino acids are available. We investigated the interplay between TORC1 signaling, autophagy, and stress adaptation, to understand these phenotypes. Amino acid or nitrogen starvation, as well as oxidative stress, inactivate TORC1, and translation inhibition through eIF2α phosphorylation occurs during all stresses. We show that both major phenotypes of autophagy-deficient cells - their failure to resume growth after amino acid starvation and their mating defects - are alleviated by genetic or environmental enhancement of intracellular amino acid pools. Regarding leucine starvation, deletion of any1 rescues the growth defect of atg1Δ mutants by maintaining amino acid transporters at the plasma membrane, promoting amino acid uptake. Regarding mating defects, TORC1 inactivation by nitrogen depletion drives cell cycle remodeling for meiotic entry, and autophagy is specifically required for the final G2-to-G1 arrest, which correlates with accumulation of the CDK inhibitor Rum1. Metabolomic analyses reveal that intracellular amino acid pools decrease sharply during nitrogen starvation, especially in autophagy-deficient cells, and supplementation with trace amino acids restores their ability to complete the final G2-to-G1 transition. Overall, our findings demonstrate that autophagy sustains intracellular amino acid pools during prolonged stress, enabling TORC1 reactivation and cell cycle remodeling required for mating and meiosis.