Two novel flavi-like viruses shed light on the plant infecting koshuviruses

Abstract

The family Flaviviridae is composed of viruses with a positive sense single-stranded RNA genome and includes viruses that are important veterinary and human pathogens. Most members of the family are arthropod and vertebrate-infecting viruses but more recently flavi-like divergent viruses have been identified in marine invertebrate and vertebrate hosts. The striking discovery of gentian Kobu-sho-associated virus (GKaV) expanded the host range of flaviviruses to plants, which was complemented by a recently reported flavi-like virus in carrot, suggesting they could be grouped in a proposed Koshovirus genus. Here, we report the identification in transcriptomic datasets and characterization of two novel RNA viruses from the flowering plants Coptis teeta and Sonchus asper, which have genetic and evolutionary affinity to koshoviruses. These two new viruses are members of novel species which were dubbed Coptis flavi-like virus 1 (CopV1) and Sonchus flavi-like virus 1 (SonV1) and with a viral monopartite RNA of ca. 24 kb, likely have the longest genomes among plant-associated RNA viruses yet. Structural and functional annotations of the polyproteins of all koshoviruses resulted in the detection not only of the expected helicase and RNA-dependent RNA polymerase, but also several additional divergent domains such as AlkB oxigenase, Trypsin-like serine protease, methyltransferase, and envelope E1 flavi-like domains. Phylogenetic analysis groups in a monophyletic clade CopV1, SonV1, GKaV and the carrot flavi-like virus robustly supporting the recently proposed genus Koshovirus of plant infecting flavi-like viruses.