|Title||Identification of a molecular pH sensor in coral|
|Publication Type||Journal Article|
|Year of Publication||2017|
|Authors||Barott KL, Barron ME, Tresguerres M|
|Journal||Proceedings of the Royal Society B: Biological Sciences|
Maintaining stable intracellular pH (pHi) is essential for homeostasis, and requires the ability to both sense pH changes that may result from internal and external sources, and to regulate downstream compensatory pH pathways. Here we identified the cAMP-producing enzyme soluble adenylyl cyclase (sAC) as the first molecular pH sensor in corals. sAC protein was detected throughout coral tissues, including those involved in symbiosis and calcification. Application of a sAC-specific inhibitor caused significant and reversible pHi acidosis in isolated coral cells under both dark and light conditions, indicating sAC is essential for sensing and regulating pHi perturbations caused by respiration and photosynthesis. Furthermore, pHi regulation during external acidification was also dependent on sAC activity. Thus, sAC is a sensor and regulator of pH disturbances from both metabolic and external origin in corals. Since sAC is present in all coral cell types, and the cAMP pathway can regulate virtually every aspect of cell physiology through post-translational modifications of proteins, sAC is likely to trigger multiple homeostatic mechanisms in response to pH disturbances. This is also the first evidence that sAC modulates pHi in any non-mammalian animal. Since corals are basal metazoans, our results indicate this function is evolutionarily conserved across animals.
This study lays the foundation for understanding the mechanisms that allow corals to detect and respond to pHi disturbances caused by both metabolic and environmental sources. The dynamic interplay of symbiont photosynthesis, coral calcification and cellular respiration involves the production and consumption of acid–base equivalents at different rates and locations within a coral throughout the diel cycle. Because sAC produces the ubiquitous messenger molecule cAMP in response to acid–base disturbances, it can potentially modulate every aspect of physiology by post-translational modifications of target proteins. Thus, the role of sAC in coral physiology is likely critical for the many essential processes that depend on CO2, pH and [Embedded Image] . This type of fundamental mechanistic understanding of coral biology is also essential for predicting how corals will fare in the face of global climate change. Finally, the observation of sAC-dependent pHi sensing in corals, similar to that found in mammalian cells, confirms sAC is an evolutionarily conserved acid–base sensor.