Transcription of genes involved in bleaching of a coral reef species Acropora downingi (Wallace, 1999) in response to high temperature

Abstract

Anthropogenic-induced global warming poses a significant threat to coral reef ecosystems worldwide. However, certain species within the Persian Gulf exhibit remarkable resilience to elevated temperatures compared to their counterparts in other reef systems. To understand the thermal tolerance in Persian Gulf corals and their molecular responses to extreme warm temperatures, Acropora downingi specimens collected from Larak Island were subjected to a heat shock of 34 ± 1 °C. We evaluated coral coloration, bleaching, and mRNA expression of biomarkers related to heat shock proteins (HSPs) such as Hsp70 and Hsp90, oxidative stress markers like Catalase and manganese superoxide dismutase (Cat and Mn-Sod), anti-apoptotic factors exemplified by B-cell lymphoma 2 (Bcl-2), and calcification-related genes including galaxin (Gal) after 24 h and 48 h of thermal shock exposure. Exposure of A. downingi to a 48-h heat shock at 34 °C resulted in noticeable fading of coral coloration compared to the control group. Despite this, the corals demonstrated resilience and did not undergo complete bleaching. Our findings also revealed significant increase of Hsp70, Hsp90, Cat, Mn-Sod, Bcl-2, and Gal mRNA expression after 24 h of thermal stress. However, after 48 h, transcripts for Hsp90, Cat, and Gal were observed to be decreased. These results suggest the pivotal roles played by genes involved in HSP signaling pathways, oxidative stress responses, anti-apoptosis processes, and calcification processes in the Persian Gulf coral's adaptation to thermal stress and its resistance to bleaching.