Understanding Crassostrea virginica tolerance of Perkinsus marinus through global gene expression analysis

Authors: Proestou, Dina; Sullivan, Mary; Markey Lundgren, Kathryn; BEN-HORIN, TAL - North Carolina State University; WITKOP, ERIN - Benaroya Institute; Hart, Keegan

Submitted to: Frontiers in Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2023
Publication Date: 1/19/2023
Citation: Proestou, D.A., Sullivan, M.E., Markey Lundgren, K.R., Ben-Horin, T., Witkop, E.M., Hart, K.M. 2023. Understanding Crassostrea virginica tolerance of Perkinsus marinus through global gene expression analysis. Frontiers in Genetics. https://doi.org/10.3389/fgene.2023.1054558.
DOI: https://doi.org/10.3389/fgene.2023.1054558

Interpretive Summary: Tolerance, the ability of host organisms to limit negative impacts on fitness by a pathogen, has important implications for disease management in wild and cultured shellfish populations. Until now, this critical disease response trait has been poorly defined and/or conflated with other mechanisms. Our study represents the first attempt to clearly define and measure disease tolerance in a commercially important bivalve mollusc. Variation in the rate of fitness decline with increasing parasite load was observed among families tested, suggesting dermo tolerance can be targeted for selection. The methods used to evaluate tolerance may not be practical for routine, family-based, selective breeding operations. Therefore, we performed global transcriptome analyses to identify specific differences in gene expression between tolerant and sensitive oysters that could aid the selection process. Our results indicate that the apoptotic pathway is fully executed in tolerant, but not sensitive oysters exposed to P. marinus. The mechanism by which tolerant eastern oysters overcome P. marinus suppression of apoptosis is unclear, but may involve serine protease inhibitors, tripartite motif-containing proteins, or both. Exploring mode of action through functional assays as well examining polymorphisms in these genes will be the focus of future work in order to develop a simpler way to breed for dermo tolerance.

Technical Abstract: The parasite Perkinsus marinus negatively impacts survival eastern oyster populations. Previous studies focused on oyster resistance to parasites, but tolerance also has important consequences for disease management in cultured and wild populations. In this study we measured tolerance and evaluated global expression patterns of two sensitive and two tolerant eastern oyster families experimentally challenged with distinct doses of P. marinus (0, 106, 107, and 108 parasite spores per gram wet weight, n=3-5 per family per dose). Weighted Gene Correlation Network Analysis (WGCNA) identified several modules positively correlated with increasing parasite dose, and one correlated with phenotype. Modules positively correlated with dose included enriched GO terms for hemocyte activation and cell cycle activity. Increased metabolic activity was also positively correlated with dose. The module positively correlated with the tolerant phenotype was enriched for transcripts associated with “programmed cell death” and tripartite motif-containing proteins. Differential expression analysis comparing the two tolerant families to the most sensitive in the 108 dosed group was consistent with the network analysis, but signals for “programmed cell death” and serine protease inhibitors were stronger in one tolerant family than the other, suggesting there are multiple avenues for disease tolerance. These results provide new insight for defining dermo response traits and have important implications for applying selective breeding for disease management.