Thermal Shock Induces Host Proteostasis Disruption and Endoplasmic Reticulum Stress in the Model Symbiotic Cnidarian Aiptasia

Coral bleaching has devastating effects on coral survival; arid reef ecosystem ftindiort,i but many of the fundamental cellular effects of thermal stress on cnidarian physiology are unclear. We used label-free liquid chromatography tandem mass spectrometry to compare the effects of rapidly (33.S degrees C,';24 h) and gradually'. (30 and 33.5 degrees C, 12 Clays) elevated temperatures on. the proteome of the model symbiotic anemone Aiptasia; We identified 2133 proteins in Aiptasia, 136 of which were differentially abundant between treatments.; Thermal shock, but not acclimation, resulted in significant abundance changes in 104 proteins, including those involved in protein folding and synthesis, redox homeostasis, and:central metabolism. Nineteen abundant structural proteins. showed particularly reduced abundance, demonstrating proteostasis, disruption and phtential proteih synthesis inhibition. Heat shock induced antioxidant mechanisms and proteins involved in stabilizing nascent proteins, preventing. protein aggregation arid degrading damaged proteins, which is indicative of endoplasmic reticulum stress: Host proteostasis disruption occurred before either bleaching or symbiont photoinhibition was detected, suggesting host-derived reactive oxygen species production as the proximate cause of thermal damage. The pronounced abundance changes in endoplasmic reticulum proteins associated with proteostasis and protein turnover indicate that these processes ate essential in the cellular response of symbiotic cnidarians to severe thermal stress.