Fig. 4

A.gemmifera juveniles in response to high pCO_2. (a) Dissolved inorganic carbon (CO₂, HCO₃^-, CO₃²⁺) uptake, ROS (H₂O₂, O₂∙^-) production and/or H⁺ accumulation in coral cells under high pCO₂. For calcification (CaCO₃), calicoblastic cells concentrate diffused CO₂, actively transport (orange hexagon) HCO₃^- following CO₂ hydration by carbonic anhydrase (CA), and Ca²⁺ into the extracellular calcifying medium. For photosynthesis, CO₂ and/or HCO₃^- is delivered to the coral cell containing the symbiotic Symbiodiniaceae in the oral endoderm. With increasing pCO₂ in seawater, there is a shift in the carbonate chemical equilibrium, leading to an accumulation of internal H⁺ in the cells in the absence of photosynthesis, ROS production of H₂O₂ and/or O₂∙^-from mitochondria and/or Symbiodiniaceae in host cells. (b) Schematic response in the coral nucleus to OA stress. (c) Autophagy-lysosomal pathways of macroautophagy, microautophagy and mitophagy fusing with lysosome and/or endosome in coral cell. (d) Molecular mechanism of the delayed cell cycle in coral cells at 3 d p.s.. Mitosis phase is divided into prophase, prometaphase, metaphase, anaphase, and telophase. The encircled P’s indicate phosphorylation. (e) Tables from left to right show the up-regulated (red), down-regulated (green), and/or up- and down-regulated (yellow) DEGs (Table S2-2), with expression variation of log₂ fold change involved in (a), (c) and (d), respectively.