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

Abstract

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 host/parasite interactions at a molecular level 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. glomeratas 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 encoding proteins involved in pathogen recognition and immune response signalling, such as galectin-4-like and G-protein coupled receptors, were significantly differentially expressed in S. glomerata infected with M. sydneyi, suggesting involvement in the hosts immune responses. Moreover, the upregulation of cytochrome P450 family genes indicate increases in the hosts detoxification processes and metabolic pathways, a possible 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. glomeratas 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. HighlightsO_LIM. sydneyi infection induces a large transcriptional response in S. glomerata C_LIO_LIUpregulation of pathogen recognition genes, including galectins, occurs in infected tissues. C_LIO_LILack of differential expression of apoptosis genes suggests other immune strategies. C_LIO_LIG-protein coupled receptor pathways were upregulated, indicating species-specific responses. C_LIO_LIResults suggest possible suppression of host immune responses by the parasite. C_LI