A Network Approach to White Band Disease Challenged Staghorn Coral microRNAs and Their Targets.

Coral reefs are increasingly threatened by disease outbreaks, yet little is known about the genetic mechanisms underlying disease resistance. Since the 1970s, White Band Disease (WBD) has decimated the Caribbean staghorn coral . However, 15% or more of individuals are highly disease-resistant, and the genes controlling the production of Argonaut proteins, involved in microRNA (miRNA) post-transcriptional gene silencing, are up-regulated in WBD-resistant corals. This suggests that miRNAs may be key regulators of coral immunity. In this study, we conducted an in situ disease transmission experiment with five healthy-exposed control tanks and five WBD-exposed tanks, each containing 50 genotypes, sampled over 7 days and then sequenced miRNAs from 12 replicate genotypes, including 12 WBD-exposed and 12 healthy-exposed control fragments from two time points. We identified 67 miRNAs in , 3 of which are differentially expressed in disease-resistant corals. We performed a phylogenetic comparison of miRNAs across cnidarians and found greater conservation of miRNAs in more closely related taxa, including all three differentially expressed miRNAs being conserved in more than one coral. One of the three miRNAs has putative genomic targets involved in the cnidarian innate immunity. In addition, community detection coupled with over-representation analysis of our miRNA-messenger RNA (mRNA) target network found two key unique miRNAs regulating multiple important immune-related pathways such as Toll-like receptor pathway, endocytosis, and apoptosis. These findings highlight how multiple miRNAs may help the coral host maintain immune homeostasis in the presence of environmental stress including disease.