Fig. 4: Schematic proposed model of slowed bleaching in corals with compromised pa-BAK.
From: BAK knockdown delays bleaching and alleviates oxidative DNA damage in a reef-building coral
pa-BAK is inserted into the mitochondrial membrane, where it contributes to the formation of the mitochondrial permeability transition pore (mPTP). This pore allows reactive oxygen species (ROS) to exit into the cytoplasm, helping to prevent mitochondrial damage. Under heat stress (A), the resulting excess of ROS activates the ROS-sensitive AMPK/Foxo3a signaling pathway, which initially triggers the expression of antioxidant genes via the Nrf2/ARE pathway. However, prolonged activation may shift the response toward programmed cell death and increased organismal stress, ultimately contributing to coral bleaching through the loss of symbiotic algae. In contrast, corals with downregulated pa-BAK (B) exhibit reduced mPTP formation in the mitochondrial membrane, limiting the release of ROS into the cytoplasm. This altered ROS signaling results in a different pattern of AMPK/Foxo3a pathway activation and appears to delay or reduce the bleaching response under heat stress.
