Intracellular pH regulation: characterization and functional investigation of H+ transporters in Stylophora pistillata

Background: Reef-building corals regularly experience changes in intra and extracellular H+ concentration ([H+]) due to physiological and environmental processes. Stringent control of [H+] is required for the maintenance of homeostatic acid-base balance in coral cells and is achieved through the regulation of intracellular pH (pHi). This task is especially challenging for reef-building corals that share an endosymbiotic relationship with photosynthetic dinoflagellates (family Symbiodinaceae), which exert a significant effect on the pHi of coral cells. Despite their importance, the pH regulatory proteins involved in the homeostatic acid-base balance have been scarcely investigated in corals. Here, we reported the full characterisation in terms of genomic structure, domain topology and phylogeny of three majors H+ transporter families implicated in pHi regulation; we investigated their tissue-specific expression and we assessed the effect of seawater acidification on their level of expression.

Results: We identified members of the Na+/Hexchanger (SLC9), vacuolar-type electrogenic H+-ATP hydrolases (V-ATPase) and voltage-gated proton channels (HvCN) families in the genome and transcriptome of S. pistillata. In addition, we identified a novel member of the HvCN gene family in the cnidarian subclass Hexacorallia, which has never been described in any species to date. We also reported key residues that participate to the H+ transporters substrate specificity, protein function and regulation. Lastly, we demonstrated that some of these have different tissue expression patterns and are mostly unaffected by exposure to seawater acidification.

Conclusions: In this study, we provide the first characterization of the Htransporters genes that contribute to homeostatic acid-base balance in coral cells. This work will enrich knowledge about basic aspects of coral biology, bearing important implications for our understanding of how corals regulate their intracellular environment.

Capasso L., Ganot P., Planas-Bielsa V., Tambutté S. & Zoccola D., in review. Intracellular pH regulation: characterization and functional investigation of H+ transporters in Stylophora pistillata. BMC Molecular and Cell Biology. Article.

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