The Role of Peroxisomes in the Stress Tolerance of the Methylotrophic Yeast 'Ogataea polymorpha' at the Transition into Anhydrobiosis

Peroxisomes are dynamic organelles involved in multiple metabolic pathways that respond to cellular and environmental conditions. Yeasts are a useful model for peroxisome studies, as their growth in media containing peroxisome proliferators, such as methanol, induces peroxisome biogenesis. We analyzed Ogataea polymorpha strains defective in peroxisome biogenesis (pex3Δ) or peroxisomal matrix protein import (pex6Δ). The mutant strains differed in their ability to survive dehydration and rehydration after incubation in peroxisome-inducing conditions, but these differences were not related to resistance to oxidative, hyperosmotic, or heat stress. These results indicate that peroxisomes support efficient entry into anhydrobiosis and subsequent recovery through a mechanism that is independent of general stress tolerance. We hypothesized that this effect is mediated by autophagic processes required for the removal of damaged organelles during desiccation. To test this hypothesis, we compared cells with basal peroxisome levels to cells with increased peroxisome numbers following the induction of peroxisome division. Autophagy was inhibited indirectly by disrupting vacuolar acidification with ammonium chloride. This strategy enabled us to explore how the peroxisome abundance and autophagic activity affect the ability of cells to enter anhydrobiosis and survive recovery.