Comparative Analysis of ROS Network Genes inExtremophile Eukaryotes

he reactive oxygen species (ROS) gene network, consisting of both ROS-generatingand detoxifying enzymes, adjusts ROS levels in response to various stimuli. We performeda cross-kingdom comparison of ROS gene networks to investigate how they have evolvedacross all Eukaryotes, including protists, fungi, plants and animals. We included the genomesof 16 extremotolerant Eukaryotes to gain insight into ROS gene evolution in organisms thatexperience extreme stress conditions. Our analysis focused on ROS genes found in all Eukaryotes(such as catalases, superoxide dismutases, glutathione reductases, peroxidases and glutathioneperoxidase/peroxiredoxins) as well as those specific to certain groups, such as ascorbate peroxidases,dehydroascorbate/monodehydroascorbate reductases in plants and other photosynthetic organisms.ROS-producing NADPH oxidases (NOX) were found in most multicellular organisms, althoughseveral NOX-like genes were identified in unicellular or filamentous species. However, despite theextreme conditions experienced by extremophile species, we found no evidence for expansion ofROS-related gene families in these species compared to other Eukaryotes. Tardigrades and rotifersdo show ROS gene expansions that could be related to their extreme lifestyles, although a highrate of lineage-specific horizontal gene transfer events, coupled with recent tetraploidy in rotifers,could explain this observation. This suggests that the basal Eukaryotic ROS scavenging systems aresufficient to maintain ROS homeostasis even under the most extreme conditions