Thermal Stress Triggers Broad Pocillopora damicornis Transcriptomic Remodeling, while Vibrio coralliilyticus Infection Induces a More Targeted Immuno-Suppression Response

Abstract

Global change and its associated temperature increase has directly or indirectly changed the distributions of hosts and pathogens, and has affected host immunity, pathogen virulence and growth rates. This has resulted in increased disease in natural plant and animal populations worldwide, including scleractinian corals. While the effects of temperature increase on immunity and pathogen virulence have been clearly identified, their interaction, synergy and relative weight during pathogenesis remain poorly documented. We investigated these phenomena in the interaction between the coral Pocillopora damicornis and the bacterium Vibrio coralliilyticus, for which the infection process is temperature-dependent. We developed an experimental model that enabled unraveling the effects of thermal stress, and virulence vs. non-virulence of the bacterium. The physiological impacts of various treatments were quantified at the transcriptome level using a combination of RNA sequencing and targeted approaches. The results showed that thermal stress triggered a general weakening of the coral, making it more prone to infection, non-virulent bacterium induced an ‘efficient’ immune response, whereas virulent bacterium caused immuno-suppression in its host.

Impacts of temperature and lunar day on gene expression profiles during a monthly reproductive cycle in the brooding coral Pocillopora damicornis

“…Temperature did not impact gene expression as a main effect; however, it did have an impact on gene expression, in the context of lunar day. Although we did not visually observe a bleaching response (loss of endosymbiotic algae), similar to a previous study conducted on P. damicornis in Taiwan where bleaching was not observed at temperatures <31.5°C (Mayfield, Chen, et al., ), previously described signatures of thermal stress such as an upregulation of genes involved with apoptosis, calcium ion homeostasis and cell differentiation were observed (Barshis et al., ; Meyer et al., ; Vidal‐Dupiol et al., ; Weis, ). This suggests that although the high temperature treatment in this study did not result in a phenotypic stress response, the prolonged elevated temperature had an effect at the transcriptional level.…”

Antimicrobial peptides in marine invertebrate health and disease

“…Similarly, immune suppression of AMPs was reported in the coral P. damicornis, in which V. coralliilyticus exhibits temperaturedependent virulence, resulting in coral bleaching above 248C and tissue lysis above 258C [7]. In its non-virulent state (below 248C), V. coralliilyticus induces the transcription of several coral immune genes [99] and the release of damicornin in coral mucus [43]. By contrast, in its virulent state, vibrios penetrating into coral tissues [100] induce a strong transient expression followed by a dramatic repression of damicornin transcription [43].…”

The early stages of the immune response of the European abalone Haliotis tuberculata to a Vibrio harveyi infection

“…Moreover, they may induce a repression effect on immune function via an alteration of cellular capacities or molecular effector synthesis, as described in the Manila clam Ruditapes philippinarum infected by Vibrio tapetis, and in the shrimp Litopenaeus vannamei following a V. alginolyticus injection Brulle et al, 2012;Li et al, 2008). Interestingly, a significant immunosuppression, including the downexpression of antimicrobial synthesis, has also been observed in the coral Pocillopora damicornis infected by Vibrio coralliilyticus (Vidal-Dupiol et al, 2014) .…”