Differential basal expression of immune genes confers Crassostrea gigas resistance to Pacific oyster mortality syndrome

Background

As a major threat to the oyster industry, Pacific Oyster Mortality Syndrome (POMS) is a polymicrobial disease affecting the main oyster species farmed across the world. POMS affects oyster juveniles and became panzootic this last decade, but POMS resistance in some oyster genotypes has emerged. While we know some genetic loci associated with resistance, the underlying mechanisms remained uncharacterized. So, we developed a comparative transcriptomic approach using basal gene expression profiles between different oyster biparental families with contrasted phenotypes when confronted to POMS (resistant or susceptible).

Results

We showed that POMS resistant oysters show differential expression of genes involved in stress responses, protein modifications, maintenance of DNA integrity and repair, and immune and antiviral pathways. We found similarities and clear differences among different molecular pathways in the different resistant families. These results suggest that the resistance process is polygenic and partially varies according to the oyster genotype.

Conclusions

We found differences in basal expression levels of genes related to TLR-NFκB, JAK-STAT and STING-RLR pathways. These differences could explain the best antiviral response, as well as the robustness of resistant oysters when confronted to POMS. As some of these genes represent valuable candidates for selective breeding, we propose future studies should further examine their function.

Oyster disease in a changing environment: Decrypting the link between pathogen, microbiome and environment

Shifting environmental conditions are known to be important triggers of oyster diseases. The mechanism(s) behind these synergistic effects (interplay between host, environment and pathogen/s) are often not clear, although there is evidence that shifts in environmental conditions can affect oyster immunity, and pathogen growth and virulence. However, the impact of shifting environmental parameters on the oyster microbiome and how this affects oyster health and susceptibility to infectious pathogens remains understudied. In this review, we summarise the major diseases afflicting oysters with a focus on the role of environmental factors that can catalyse or amplify disease outbreaks. We also consider the potential role of the oyster microbiome in buffering or augmenting oyster disease outbreaks and suggest that a deeper understanding of the oyster microbiome, its links to the environment and its effect on oyster health and disease susceptibility, is required to develop new frameworks for the prevention and management of oyster diseases.