Plasticity, Paralogy and Pseudogenization: Rhabdoviruses of Freshwater Mussels Elucidate Mechanisms of Viral Genome Diversification and the Evolution of the Finfish-Infecting Rhabdoviral Genera

Killamcar Virus 1 (KILLV-1) from Lampsilis cardium and Chemarfal Virus 1 (CHMFV-1) from Margarutufera falcata were the first two Rhabdovirus reported in mollusks. These two novel viruses highlight an uncommon example of Rhabdoviral plasticity among negative-sense RNA viruses. Based on sequence analysis with phylogenetic interferences and analyses of transcriptional regulation, KILLV-1 is an Alpharhabdovirus. KILLV-1 developed and diverged due to glycoprotein gene duplication processing to a new gene paralog, increasing its genome size and complexity, which separates KILLV-1 from Scophravirus, a closely related virus. CHMFV-1 belongs to the family of Gammarhabdovirinae. It closely relates to Novirhabdovirus owing to its comparatively longer genome size and lower GC content. Intriguingly, CHMFV-1 also carries a pseudogenized version of Non virion (NV) genes that encoded for NV proteins, which is essential for the establishment of antiviral state during the Novirhabdovirus infection of fish. This discovery suggests that the origin of NV protein occurred beforehand to the divergence of Novirhabdovirus and CHMFV-1 because these viruses contain NV gene. Furthermore, because most Rhabdoviruses are mostly found in vertebrate animals like finfish, host switching from finfish to freshwater mussels theoretically occurs when freshwater mussels’ larvae parasitize on finfish and consume fish blood and tissues.

(HW)