ASSESSING THE ROLE OF CASPASE ACTIVITY AND METACASPASE EXPRESSION ON VIRAL SUSCEPTIBILITY OF THE COCCOLITHOPHORE, EMILIANIA HUXLEYI (HAPTOPHYTA)

摘要

As part of their strategy to infect the globally important coccolithophore, Emiliania huxleyi(Lohmann) W.W. Hay & H.P. Mohler, Coccolithoviruses trigger and regulate the host’s programmed cell death (PCD) machinery during lytic infection. The induction and recruitment of host metacaspases, specialized, ancestral death proteases that facilitate viral lysis, suggests they may be important subcellular determinants to infection. We examined the “basal” levels and patterns of caspase activity and metacaspase expression in exponentially growing resistant and sensitive E. huxleyi strains and linked them with susceptibility to E. huxleyi virus 1 (EhV1). Resistant E. huxleyi strains were consistently characterized by low caspase specic activity and a relatively simple metacaspase expression prole. In contrast, sensitive E. huxleyi strains had markedly elevated caspase specic activity and consistently expressed more diverse metacaspase proteins. Using pooled data sets from triplicate experiments, we observed statistically signicant linear correlations between infectivity, caspase activity, and metacaspase expression, with each strain forming distinct clusters, within a gradient in viral susceptibility. At the same time, we observed positive correlations between the expression of a subset of metacaspase proteins and lower susceptibility, suggestive of potential protective roles. Our ndings implicate the importance of subtle differences in the basal physiological regulation of the PCD machinery to viral resistance or sensitivity and cell fate.