Breaking dormancy in spores of budding yeast transforms its cytoplasm and the solubility of its proteome

Abstract

The biophysical properties of the cytoplasm are major determinants of key cellular processes and adaptation. Yeasts produce dormant spores that can withstand extreme conditions. We show that spores exhibit extraordinary biophysical properties, including a highly viscous and acidic cytosol. These conditions alter the solubility of more than 100 proteins such as metabolic enzymes that become more soluble as spores transit to active cell proliferation upon nutrient repletion. A key regulator of this transition is the heat shock protein Hsp42, which shows transient solubilization and phosphorylation, and is essential for the transformation of the cytoplasm during germination. Germinating spores therefore return to growth through the dissolution of protein assemblies, orchestrated in part by Hsp42 activity. The modulation of spores molecular properties are likely key adaptive features of their exceptional survival capacities.

Cytoplasmic fluidization triggers breaking spore dormancy in fission yeast

“…During the germination process, the μNS mobility was gradually increased (Fig. 5C), which is consistent with a previous report on budding yeast spores (24). Within the first 2 hr of germination, μNS mobility increased about 6-fold, followed by a gradual increase in μNS mobility.…”

“…Growing evidence indicates that a liquid-like cytoplasmic property turns into a solid- or glass-like state under stress conditions, and these cytoplasmic changes have been proposed to be responsible for stress resistance and dormancy breaking (7, 24). However, the molecular basis underlying such changes in the cytoplasmic properties in response to environmental stimuli is not yet fully understood.…”

“…Dormancy is a cellular state, in which the metabolic activity is decreased and the cell cycle is reversibly arrested under unfavorable conditions (7, 24). Those characteristics link to the cytoplasmic properties of dormant cells with reduced fluidity and molecular mobility.…”

“…For example, it is known that the cytoplasms of dormant cells show a solid or glass-like properties due to their reduced water content; such characteristic cytoplasms are observed in diverse species such as bacterial spores (25, 26), fungal spores (27), plant seeds (28), tardigrades (29), and sleeping chironomids (30). Recently, micro-rheological measurements revealed that macromolecular mobility is restricted inside the cytoplasm of dormant cells (7, 19, 24). However, it remains unclear what molecular mechanisms are involved in the reversible change in cytoplasmic fluidity, and which and how intracellular signaling pathways govern these processes.…”

“…As another example, upon temperature increase, budding yeast cells synthesize trehalose and glycogen to increase cytoplasmic viscosity, which counteracts the increase in protein diffusivity (23). Dormancy is a cellular state, in which the metabolic activity is decreased and the cell cycle is reversibly arrested under unfavorable conditions (7,24). Those characteristics link to the cytoplasmic properties of dormant cells with reduced fluidity and molecular mobility.…”