Population-specific transcriptomics of Pacific oyster after exposure to a highly pathogenic, globally distributed virus.

Disease outbreaks in marine invertebrates, particularly in cultivated species, have increased as stressful environmental conditions become more frequent. The Ostreid herpesvirus and its microvariants have caused substantial mortalities in Pacific oysters globally, heavily impacting aquaculture production in localities where the virus becomes established. This study investigates the molecular response of Pacific oysters to OsHV-1 μVar infection in two oyster populations: a population of Miyagi oysters, and a population of Midori oysters. Although viral infection elicited a general and significant up-regulation of antiviral defense transcripts that was very similar in both populations and that included RIG-I like receptors and the interferon-like pathway, gene-wise clustering analyses clearly differentiated both populations. Among differences between Midori and Miyagi were several immunity-related genes and histone-coding genes that indicated possible pre-transcriptional mechanisms of gene regulation influencing disease outcomes. Among other differences, genes encoding for viral sensing proteins (SAMD9 and NFX-1 zinc finger) showed higher basal and infection-induced expression in Midori, whereas Miyagi oysters exhibited greater up-regulation of ubiquitination pathways. We also compared the general response of Pacific oysters to different OsHV-1 μVars strains, concluding that there is no marked difference between the oyster response to a U.S. OsHV-1 μVar compared to an Australian μVar. These results are important for future work that focuses on developing Pacific oysters that are tolerant to OsHV-1 μVars and to develop additional management strategies to prevent the spread of this viral disease.