Stress-induced remodeling of membrane-bound organelles in budding yeast.

Membrane-bound organelles undergo extensive remodeling during environmental stress, yet systematic side-by-side comparisons of organelle responses in budding yeast remain limited. Here, a panel of fluorescent markers was used to examine multiple organelles in Saccharomyces cerevisiae exposed to heat, hydrogen peroxide, acetic acid, or ethanol. Across all conditions, mitochondria consistently shifted from tubular networks to fragmented puncta, representing a common stress response. Quantitative scoring showed that heat stress induced mitochondrial fragmentation in more than 90% of cells within 20 min, and GFP-HDEL redistribution was detected in a substantial fraction of cells under all four stress conditions, with the strongest effect under heat stress. In contrast, overall endoplasmic reticulum (ER) morphology remained largely preserved, although redistribution of GFP-HDEL indicated altered ER retention and/or endomembrane homeostasis. Heat and oxidative stress also induced Ire1 puncta. Several nuclear proteins exhibited stress-dependent redistribution from the nucleus, indicating dynamic remodeling of nuclear protein localization. Vacuoles generally appeared enlarged and fused, whereas acetic acid induced a distinct phenotype with Ybh3 enrichment at the vacuolar membrane and redistribution of Prc1 and Pep4 to cytoplasmic puncta. Markers of the early and late Golgi and the late endosome showed stress-specific loss, clustering, or relocalization. Lipid droplets, peroxisomes, and autophagy-related structures were also altered. Additionally, Yca1, Aif1, and Mmi1 formed puncta under heat and ethanol stress. Together, these findings provide a comparative imaging framework defining shared and stress-specific features of organelle remodeling in budding yeast.