Ambiviricota , a novel ribovirian phylum for viruses with viroid-like properties

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Kuhn, Jens, H | Botella, Leticia | de la Peña, Marcos | Vainio, Eeva, J | Krupovic, Mart | Lee, Benjamin, D | Navarro, Beatriz | Sabanadzovic, Sead | Simmonds, Peter | Turina, Massimo

Edité par CCSD ; American Society for Microbiology -

International audience. Fungi harbor a vast diversity of mobile genetic elements (MGEs). Recently, novel fungal MGEs, tentatively referred to as ‘ambiviruses,’ were described. ‘Ambiviruses’ have single-stranded RNA genomes of about 4–5 kb in length that contain at least two open reading frames (ORFs) in non-overlapping ambisense orientation. Both ORFs are conserved among all currently known ‘ambiviruses,’ and one of them encodes a distinct viral RNA-directed RNA polymerase (RdRP), the hallmark gene of ribovirian kingdom Orthornavirae . However, ‘ambivirus’ genomes are circular and predicted to replicate via a rolling-circle mechanism. Their genomes are also predicted to form rod-like structures and contain ribozymes in various combinations in both sense and antisense orientations—features reminiscent of viroids, virusoids, ribozyvirian kolmiovirids, and yet-unclassified MGEs (such as ‘epsilonviruses,’ ‘zetaviruses,’ and some ‘obelisks’). As a first step toward the formal classification of ‘ambiviruses,’ the International Committee on Taxonomy of Viruses (ICTV) recently approved the establishment of a novel ribovirian phylum, Ambiviricota , to accommodate an initial set of 20 members with well-annotated genome sequences.

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