ROS Signaling and NADPH Oxidase in Red Algae.

We explore the diverse roles of reactive oxygen species (ROS) and NADPH oxidases in red algae, focusing on their involvement in fertilization, wound repair, stress adaptation, and development. Once considered mere metabolic byproducts, ROS are now recognized as pivotal signaling molecules in red algae. ROS are actively produced and regulated by NADPH oxidase homologs in red algae. During fertilization, ROS facilitate gamete recognition and post-fertilization cell wall development. NADPH oxidase-produced ROS also play essential roles in wound repair, aiding cellular migration and cytoskeletal reorganization at injury sites. A survey of NADPH oxidase homologs in transcriptomic and genomic datasets shows that NADPH oxidase homologs have a long evolutionary history in red algae, with some orthologs duplicating before the split of the Bangiophyceae-Flordeophyceae, approximately 1.1 billion years ago. Additionally, we discuss modifications in red algal NADPH oxidase genes related to calcium binding compared to plants and hypothesize that independent calcium signaling pathways are involved. These insights reveal the significance of NADPH oxidase at a molecular level in supporting red algae's physiological processes and adaptive strategies.