Auto-recoding A-to-I RNA editing sites in Adar gene underwent compensatory gains and losses in major insect clades.

As one of the most prevalent RNA modifications in animals, adenosine-to-inosine (A-to-I) RNA editing facilitates environmental adaptation of organisms by diversifying the proteome in a temporal-spatial manner. In flies and bees, the editing enzyme Adar has independently gained two different auto-recoding sites that form an auto-feedback loop, stabilizing the overall editing efficiency. This ensures cellular homeostasis by keeping the normal function of target genes. However, in a broader range of insects, it is unclear about the evolutionary dynamics and significance of this Adar auto-regulatory mechanism. We retrieved the genomes of 377 arthropod species covering the five major insect orders (Hemiptera, Hymenoptera, Coleoptera, Diptera, and Lepidoptera) and aligned the Adar auto-recoding sites across all genomes. We found that the two auto-recoding sites underwent compensatory gains and losses during the evolution of two orders with most sequenced species (Diptera and Hymenoptera) and that the two editing sites were mutually exclusive among them: one editable site is significantly linked to another uneditable site. This auto-recoding mechanism of Adar could flexibly diversify the proteome and stabilize the global editing activity. Many insects independently selected different auto-recoding sites to achieve a feedback loop and regulate the global RNA editome, revealing an interesting phenomenon during evolution. Our study reveals the evolutionary force acting on the accurate regulation of RNA editing activity in insects and thus deepens our understanding on the functional importance of RNA editing in environmental adaptation and evolution.