Innate immune gene expression inAcropora palmatais consistent despite variance in yearly disease events

Abstract

Coral disease outbreaks are expected to increase in prevalence, frequency and severity due to climate change and other anthropogenic stressors. This is especially worrying for the Caribbean branching Acropora palmata which has already seen an 80% decrease in its coral cover, with this primarily due to disease. Despite the importance of this species, there has yet to be a characterization of its transcriptomic response to disease exposure. In this study we provide the first transcriptomic analysis of 12 A. palmata genotypes, and their symbiont Symbiodiniaceae, exposed to disease in 2016 and 2017. Year was the primary driver of sample variance for A. palmata and the Symbiodiniaceae. Lower expression of ribosomal genes in the coral, and higher expression of transmembrane ion transport genes in the Symbiodiniaceae indicate that the increased virulence in 2017 may have been due to a dysbiosis between the coral and Symbiodiniaceae. We also identified a conserved suite of innate immune genes responding to the disease challenge that was activated in both years. This included genes from the Toll-like receptor and lectin pathways, and antimicrobial peptides. Co-expression analysis identified a module positively correlated to disease exposure rich in innate immune genes, with D-amino acid oxidase, a gene implicated in phagocytosis and microbiome homeostasis, as the hub gene. The role of D-amino acid oxidase in coral immunity has not been characterized but holds potential as an important enzyme for responding to disease. Our results indicate that A. palmata mounts a similar immune response to disease exposure as other coral species previously studied, but with unique features that may be critical to the survival of this keystone Caribbean species.

The coral symbiontCandidatusAquarickettsia is variably abundant in threatened Caribbean acroporids and transmitted horizontally

“…Assuming the proportion of A. rohweri to host reads are indeed reflective of infection status [75][76][77], relative resistance of Ac. palmata may be attributed to environmental factors such as depth, innate host immunity, or defenses mounted by the host microbiome [78][79][80]. Determining which factors may be leading to resistance in Ac.…”

The Complicated Evolutionary Diversification of the Mpeg-1/Perforin-2 Family in Cnidarians

“…Two scleractinian coral transcriptomic datasets were mined for homologs of P2; one from Pocillopora damicornis exposed to the synthetic immune stimulus lipopolysaccharide (LPS), NCBI SRA BioProject PRJNA587509, (34) and the second from Acropora palmata exposed to the naturally occurring white band disease (WBD); NCBI SRA BioProject PRJNA529682, (42); Figure 1D. In P. damicornis, one Mpeg-1 homolog was found to be significantly upregulated (pdam_00017055, LFC = 1.21), while in A. palmata two paralogs of Mpeg-1 were found to be significantly downregulated in response to WBD (Apalm_v2_evm.model.Sc0a5M3_382_HRSCAF_692.340, LFC = −1.38; Apalm_v2_evm.model.Sc0a5M3_382_HRSCAF _692.335, LFC = −0.94).…”

“…With the presence of multiple paralogs, it is possible that some of these genes are not involved in innate immunity. Additionally, the variation in gene expression in A. palmata could be due to environmental challenges, as these were nursery reared corals (42). Further investigation into the function of these genes in multiple species of coral will be valuable for our understanding of the functional repertoire of this gene family in cnidarians, as well as, the effects of environmental stress.…”