Abstract
Coral reefs are declining worldwide due to multiple factors including rising sea surface temperature, ocean acidification, and disease outbreaks. Over the last 30 years, White Band Disease (WBD) alone has killed up to 95% of the Caribbean`s dominant shallow-water corals—the staghorn coral Acropora cervicornis and the elkhorn coral A. palmata. Both corals are now listed on the US Endangered Species Act, and while their recovery has been slow, recent transmission surveys indicate that more than 5% of staghorn corals are disease resistant. Here we compared transcriptome-wide gene expression between resistant and susceptible staghorn corals exposed to WBD using in situ transmission assays. We identified constitutive gene expression differences underlying disease resistance that are independent from the immune response associated with disease exposure. Genes involved in RNA interference-mediated gene silencing, including Argonaute were up-regulated in resistant corals, whereas heat shock proteins (HSPs) were down-regulated. Up-regulation of Argonaute proteins indicates that post-transcriptional gene silencing plays a key, but previously unsuspected role in coral immunity and disease resistance. Constitutive expression of HSPs has been linked to thermal resilience in other Acropora corals, suggesting that the down-regulation of HSPs in disease resistant staghorn corals may confer a dual benefit of thermal resilience.
Highlights
Coral reefs are the world’s most biodiverse marine ecosystems, hosting approximately 25% of all marine species [1]
Transcriptome-wide analysis of the gene expression patterns underlying disease resistance in the staghorn coral A. cervicornis demonstrates that resistance to White Band Disease (WBD) infection is conferred by the constitutive expression of multiple gene pathways, including up-regulation of RNA interference-mediated gene silencing (RNAi)-mediated gene silencing and down-regulation of heat shock proteins (HSPs)
It is possible that WBD infection involves both bacterial and viral pathogens [9], and that the up-regulation of Argonaute in resistant corals is being used to respond to exogenous double-stranded RNA via small interfering RNA (siRNA)
Summary
Coral reefs are the world’s most biodiverse marine ecosystems, hosting approximately 25% of all marine species [1]. Reef-building corals provide the foundation for these diverse communities, but are highly vulnerable to environmental stressors and anthropogenic impacts including rising sea surface temperatures, ocean acidification and disease outbreaks associated with climate change [2, 3]. It has been estimated that one third of world’s reef-building corals are at risk of extinction [4]. Recent studies indicate that some corals have a better ability to recover from bleaching events and disease outbreaks [5, 6] highlighting the importance of understanding the mechanisms of resilience and resistance in coral reef restoration and conservation.
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