Mitochondrial DNA damage, repair and copy number dynamics of Sclerophytum sp. (Anthozoa: Octocorallia) in response to short-term abiotic oxidative stress

As a consequence of global climate change, the increasing frequency of environmental disturbances and surplus oxidative stress experienced by coral reefs will likely contribute to phase shifts from stony to soft corals. Mitochondrial response to reactive oxygen species (ROS) -induced oxidative damage appears pivotal for bioenergetic adaptation and recovery during environmental stress, partly governed by mitochondrial DNA copy number. Unlike other animals, octocorals possess unique mitogenomes with an intrinsic DNA mismatch repair gene, the mtMutS, that is likely to have a role in mitochondrial response and mtDNA damage recovery. Yet, there is a general lack of stress response studies on octocorals from a mitochondrial perspective. Here we evaluate the mitochondrial response of the octocoral Sclerophytum sp. subjected to acute elevated temperature and low pH, and its putative competence to reverse oxidative mtDNA damage caused by exogenous agents like hydrogen peroxide (H 2 O 2 ). Temporal changes in mtDNA copy number and mtDNA damage and recovery were monitored. Both short-term thermal and low pH stress applied independently instigated mtDNA damage and affected mtDNA copy number differently, while mtMutS gene was significantly upregulated during low pH stress. mtDNA damage caused by H 2 O 2 insult was observed to be promptly reversed in Sclerophytum sp., and a higher mtDNA copy number was associated with lower mtDNA damage. These findings provide insights into the potential role of mtMutS gene in conferring resilience to octocorals, the relevance of mtDNA copy number, and emphasize the importance of better understanding the mitochondrial stress response of cnidarians in the context of climate change. • Octocorals possess unique mitochondrial genomes with an intrinsic DNA mismatch repair gene, mtMutS . • Short-term thermal and low pH stress cause mtDNA damage and variation in mtDNA copy number in the soft coral Sclerophytum sp. • mtMutS gene was significantly upregulated during low pH stress. • mtDNA damage caused by H 2 O 2 was quickly reversed, suggesting efficient mtMutS DNA repair activity. • Higher mtDNA copy number was associated with lower mtDNA damage.