A comparison of Saprolegnia parasitica gene expression in the presence and absence of a host
Date
2018
Authors
May, Emily
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Abstract
As the importance of aquaculture increases globally, determining the infection strategies of opportunistic fish pathogens like Saprolegnia parasitica grows increasingly vital. Saprolegnia parasitica, a hemibiotrophic oomycete, has an initial biotrophic stage in which it suppresses host defences to facilitate infection, but the molecular mechanisms behind this infection strategy are largely unknown. In this study, I tested the hypothesis that expression of two S. parasitica virulence genes differs in the presence and absence of a host. The studied genes were: SpHtp1, a putative RXLR-like effector gene and SPRG_13235, a potentially horizontally transferred disintegrin gene with no known oomycete analogs. To test my hypothesis, I exposed pure S. parasitica zoospore cultures either to water imbued with Salmo salar effluents or to sterile water; then, I extracted RNA from experimental samples and measured expression differences with polymerase chain reactions (PCR). I successfully used nested PCR with gene-specific primers to qualitatively analyze expression, but quantitative analyses with real-time PCR (qPCR) were unsuccessful. Based on qualitative analyses, I concluded that SPRG_13235 was expressed in low amounts in both host presence and host absence, implying that factors other than host presence mediate gene expression variance. I was unable to determine whether SpHtp1 expression varied. Future studies should consider both studied genes but should focus on SPRG_13235, which remains largely uncharacterized. Disintegrin proteins inhibit vital cell functions by blocking integrin ligand-binding domains, potentially making them vital for host infection. The SPRG_13235 primer sets designed in this study can be used to facilitate future research in this area and can also be used to effectively detect S. parasitica propagules in environmental samples.