Transcriptome Analyses of Immune System Behaviors in Primary Polyp of CoralAcropora digitiferaExposed to the Bacterial PathogenVibrio coralliilyticusunder Thermal Loading

Elevated sea surface temperature associated with global warming is a serious threat to coral reefs. Elevated temperatures directly or indirectly alter the distribution of coral-pathogen interactions and thereby exacerbate infectious coral diseases. The pathogenic bacteriumVibrio coralliilyticusis well-known as a causative agent of infectious coral disease. Rising sea surface temperature promotes the infection of corals by this bacterium, which causes several coral pathologies, such as bacterial bleaching, tissue lysis, and white syndrome. However, the effects of thermal stress on coral immune responses to the pathogen are poorly understood. To delineate the effects of thermal stress on coral immunity, we performed transcriptome analysis of aposymbiotic primary polyps of the reef-building coralAcropora digitiferaexposed toV. coralliilyticusunder thermal stress conditions.V. coralliilyticusinfection of coral that was under thermal stress had negative effects on various molecular processes, including suppression of gene expression related to the innate immune response. In response to the pathogen, the coral mounted various responses including changes in protein metabolism, exosome release delivering signal molecules, extracellular matrix remodeling, and mitochondrial metabolism changes. Based on these results, we provide new insights into innate immunity ofA. digitiferaagainst pathogen infection under thermal stress conditions.