Transcriptomic responses to Marteilia sydneyi infection in the sydney rock oyster Saccostrea glomerata

Marteilia sydneyi, an ascetosporean parasite, is the causative agent of Queensland Unknown (QX) disease in Saccostrea glomerata. QX disease outbreaks often lead to high mortality rates and considerable population losses. Investigating molecular host/parasite interactions is imperative to better understand how S. glomerata mounts immune defences and to explore whether M. sydneyi evades host responses. This study aims to investigate S. glomerata's response to M. sydneyi infection through differential gene expression analysis to uncover immune mechanisms and potential markers for resistance. RNA sequencing and differential gene expression analysis revealed widespread transcriptional changes between infected and non-infected oysters. Genes involved in pathogen recognition and immune response signalling, such as galectin-4-like and G-protein coupled receptors, were significantly differentially expressed in infected S. glomerata, suggesting involvement in the host's immune responses. The upregulation of cytochrome P450 family genes indicates an enhanced detoxification response to infection-induced stress. However, extracellular superoxide dismutase, a gene previously implicated in the oxidative stress response to pathogens, was significantly downregulated, suggesting potential suppression of oxidative burst defence mechanisms. These results reveal the complex nature of S. glomerata's response to M. sydneyi infection, and possible suppression or evasion of host defences by the parasite. The study also identifies multiple genes that likely play crucial roles in the molecular responses and defence mechanisms of S. glomerata to M. sydneyi infection. The identification of these genes provides potential target genes for future studies and possible biomarkers for breeding QX-resistant oyster lines.