Brener-Raffalli K. auteur aut IRD Vidal-Dupiol J. auteur aut IRD Adjeroud Mehdi auteur aut IRD Rey O. auteur aut IRD Romans P. auteur aut IRD Bonhomme F. auteur aut IRD Pratlong M. auteur aut IRD Haguenauer A. auteur aut IRD Pillot R. auteur aut IRD Feuillassier L. auteur aut IRD Claereboudt M. auteur aut IRD Magalon H. auteur aut IRD Gélin P. auteur aut IRD Pontarotti P. auteur aut IRD Aurelle D. auteur aut IRD Mitta G. auteur aut IRD Toulza E. auteur aut IRD text journalArticle eng text/pdf reformatted digital access Ecosystems worldwide are suffering from climate change. Coral reef ecosystems are globally threatened by increasing sea surface temperatures. However, gene expression plasticity provides the potential for organisms to respond rapidly and effectively to environmental changes, and would be favored in variable environments. In this study, we investigated the thermal stress response in Pocillopora coral colonies from two contrasting environments by exposing them to heat stress. We compared the physiological state, bacterial and Symbiodiniaceae communities (using 16S and ITS2 metabarcoding), and gene expression levels (using RNA-Seq) between control conditions and heat stress (the temperature just below the first signs of compromised health). Colonies from both thermal regimes remained apparently normal and presented open and colored polyps during heat stress, with no change in bacterial and Symbiodiniaceae community composition. In contrast, they differed in their transcriptomic responses. The colonies from Oman displayed a more plastic transcriptome, but some genes had a higher basal expression level (frontloading) compared to the less thermotolerant colonies from New Caledonia. In terms of biological functions, we observed an increase in the expression of stress response genes (including induction of tumor necrosis factor receptors, heat shock proteins, and detoxification of reactive oxygen species), together with a decrease in the expression of genes involved in morpho-anatomical functions. Gene regulation (transcription factors, mobile elements, histone modifications and DNA methylation) appeared to be overrepresented in the Oman colonies, indicating possible epigenetic regulation. These results show that transcriptomic plasticity and frontloading can be co-occurring processes in corals confronted with highly variable thermal regimes. specialized OMAN NOUVELLE CALEDONIE PACIFIQUE 034 038 082 021 2 e13 [26 ] 2022 2804-3871 https://www.documentation.ird.fr/hor/fdi:010089969 10.24072/pcjournal.79 2804-3871 [F B010089969] https://www.documentation.ird.fr/hor/fdi:010089969 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2024-07/010089969.pdf IRD - Base Horizon / Pleins textes 2024-05-06 2025-02-24 fdi:010089969 fre