Structural Decorations in Viruses : Unraveling Acquired Functional Structures in Icosahedral RNA Virus Capsids

Sammanfattning: Viruses have a profound impact worldwide, posing challenges to animal welfare, agriculture, human health, and the ecosystem. This thesis examines the realm of non-enveloped icosahedral double-stranded (ds)RNA and single-stranded (ss)RNA viruses through three studies. In Paper I, we employed a reverse genetics approach to generate recombinant dsRNA totivirus-like viruses—which negatively impact fisheries and the economy—unraveling the intricate relationships between viral genes and life cycles. Our reverse genetic method has proven essential for generating infectious totivirus-like virus particles, allowing for a nuanced exploration of viral behaviors. Understanding these behaviors has the potential to help in developing effective virus control approaches. In Paper II, we elucidated the previously unknown capsid structure, uncovering the intriguing acquired features of a dsRNA megabirnavirus—Rosellinia necatrix megabirnavirus 1-W779 (RnMBV1)—through cryogenic electron microscopy single-particle analysis. RnMBV1, a fungal virus, has potential applications in controlling white root rot, a plant disease that causes substantial economic losses. Insights into this viral structural information can enhance our ability to leverage this fungal virus for economic and agricultural benefits. In Paper III, we obtained the capsid atomic models of a Marnaviridae ssRNA virus: Chaetoceros socialis forma radians RNA virus 1. Additionally, we generated a structure-based phylogeny using viral protein structures predicted by AlphaFold2; this was done to enhance our understanding of algal virus-host specificity. As harmful algal blooms (HABs) pose global threats to ecology and the economy, Chaetoceros algae have emerged as a contributing factor. Certain Marnaviridae viruses exhibit specific infection patterns in Chaetoceros, thereby influencing the occurrence and mitigation of HABs. Studies on Marnaviridae viruses collectively provide insights into the interactions between algal viruses and their hosts, paving the way for utilizing marine algal viruses to address HAB-related challenges. Together, our functional and structural analyses will contribute to a broader understanding of both dsRNA and ssRNA viruses, their behaviors, and their potential applications in addressing economic, agricultural, ecological, and healthcare issues.