BAK knockdown delays bleaching and alleviates oxidative DNA damage in a reef-building coral.

As climate change threatens marine ecosystems, efforts to restore coral reefs using resilient corals are increasing. This conservation approach remains limited by our understanding of cellular mechanisms of resilience and trade-offs. Here, we demonstrate that downregulation of pa-BAK stabilizes the coral-algal endosymbiosis and slows bleaching during acute heat stress in Pocillopora acuta through coordinated expression of gene clusters. The improvement in thermal tolerance was closely related to the downregulation efficiency in individual corals. Oxidative DNA damage, a hallmark of thermal stress response, was prevented in corals with stabilized symbiosis, likely through a decrease in mitochondrial ROS release. We hypothesize that this manipulation causes a cascading molecular response, which may impact other traits such as oxidative mitochondrial damage, proving detrimental over the longer term. Developing our understanding of heat-stress defense mechanisms that promote stability in the coral-algal symbiosis is fundamental for effective modern coral reef restoration practices based on improving ecosystem resilience.