Adaptive mechanisms of the deep-sea coral Polymyces wellsi (Flabellidae, Scleractinia) illuminate strategies for global climate change

An oxygen minimum zone (OMZ) typically occurs in the tropical western Pacific and is characterized by an unfavorably low pH, a rather low oxygen content and extreme food limitation. Understanding how deep-sea corals survive in these challenging conditions, especially how calcification occurs at depths near the aragonite saturation horizon, is anticipated to provide a strategy for stony corals to address global climate change. In this study, we collected the deep-sea solitary coral Polymyces wellsi living in the OMZ of the Caroline Ridge and analyzed its mitochondrial genome and transcriptome. Phylogenetic analysis based on mitochondrial genomes suggested that the solitary character and the deep-sea adaptations evolved at least three times in Scleractinia. In comparison to the transcriptomes of shallow-water counterparts, the genetic elements related to biomineralization, mitochondrial components, and ciliary motion underwent positive selection and expansion in P. wellsi, which suggested their significance in facilitating the adaptations to the stressors of low pH, insufficient oxygen content, scarce food resources, or the combined effects of these stressors within the OMZ. An interesting finding of this study was that the positively selected amino acids in P. wellsi increased the isoelectric points of its skeleton organic matrix proteins, which suggested a novel bio-indicator that may reflect the adaptive capacity to the external acidified seawater. Overall, this study not only provides insights into the adaptive mechanisms of deepsea solitary corals but also illuminates strategies for global climate change.

Automated summary

This study analyzed the mitochondrial genome and transcriptome of deep-sea solitary coral Polymyces wellsi living in the oxygen minimum zone (OMZ) and showed the genetic mechanisms underlying its adaptation to low pH, low oxygen content, and extreme food limitation. The findings revealed positive selection and expansion of genes related to biomineralization, mitochondrial components, and ciliary motion, indicating their significance in facilitating the coral's adaptation to the stressors in the OMZ. Moreover, the study identified a novel bio-indicator, the increased isoelectric points of skeleton organic matrix proteins, which may reflect the adaptive capacity of the coral to external acidified seawater. Overall, this study provides insights into the adaptive mechanisms of deep-sea solitary corals and offers strategies for addressing global climate change.