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UBC Theses and Dissertations

The diversity, evolution and virus-derived small interfering RNAs of arthropod-associated RNA viruses Chang, Tianyi


Arthropods are the most speciose animal on the planet, they are widely distributed, and play vital roles in global ecosystems. Arthropods have intimate ecological relationships with a broad range of organisms. Accordingly, they may serve as natural reservoirs for different viruses and drive the evolution of viruses by exchanging them with other organisms. Yet, for the vast diversity of arthropods, their associated viruses remain unexplored. This thesis started by investigating RNA viruses associated with marine copepods, including parasitic species that have significant impacts on aquaculture, and planktonic species that are essential to marine food webs and global biogeochemical cycles. Then, a systematic investigation was conducted to fully explore the RNA virus diversity in arthropods, and to study their roles in the global evolution of RNA viruses. Finally, virus-derived small RNAs (viRNAs) were analyzed, aiming to characterize the RNA interference (RNAi) antiviral immunity in different arthropods, and to identify novel viruses infecting them. The thesis reports over 1400 previously unknown RNA viruses in three subphyla of the Arthropoda, encompassing 822 novel evolutionary group (75% amino acid identity), and demonstrates the central role that arthropods have played in the macroevolution of RNA viruses. Moreover, many of these newly discovered viruses are associated with arthropods that have ecological, economic, and public health significance. Additionally, by analyzing viRNAs, I show that RNAi-mediated antiviral immune pathways are commonly present in arthropods, although the size and base distributions of the resulting viRNAs are highly variable among different species. Furthermore, by screening for typical signatures of viRNAs, more than 6000 potential parasitic sequences were identified in different species of arthropods. Overall, this work reports viruses infecting important arthropod species, cements the central role of arthropods in the evolution of RNA viruses, expands the current known diversity of RNA viruses, and systematically characterizes the RNAi-mediated antiviral immunity in arthropods.

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