Subfamily: Densovirinae
Genus: Ambidensovirus
Distinguishing features
Genus Ambidensovirus was created in 2014 to combine viruses in two previous genera, Densovirus and Pefudensovirus, with a group of then-unclassified viruses that all use the same ambisense gene expression strategy. These viruses have a homotelomeric ssDNA genome of ~5.3–6 kb with terminal repeats (TRs) of <0.5 kb (Figure 3. Parvoviridae) and encapsidate both positive and negative-sense strands of genome DNA in equal numbers. The genus appears to be monophyletic (Figure 6A. Parvoviridae) and all of the viruses have a complex genetic rearrangement that allows them to co-ordinate bidirectional transcription (Figure 3. Parvoviridae), but the evolution of this ambisense organization is not fully understood and individual pairs of viruses commonly fall outside the standard >30% identity demarcation criteria. Eleven species are recognized, variously isolated from insects in orders Blattodea, Diptera, Hemiptera, Hymenoptera, Lepidoptera and Orthoptera, or from farmed decapod crayfish (Cherax quadricarinatus) or sea stars (phylum Echinodermata).
Virion
See discussion under family description (Figures 1. Parvoviridae and 2. Parvoviridae).
Genome organization and replication
NS proteins (NS1–3) are encoded in three or more ORFs on a single DNA strand that is transcribed towards the center of the genome from one or two promoters near the left-end, as illustrated in Figure 3C. Parvoviridae (Tijssen et al., 2016). NS1 and NS2 proteins are expressed by alternative splicing and leaky scanning translation, whereas NS3, when present, is expressed from an unspliced transcript. Structural proteins are encoded on the complementary strand, expressed by alternative splicing or leaky scanning of an mRNA transcribed towards the center of the genome from a single promoter at map unit 90. NS and VP transcripts have a short overlap in the center of the genome, which encompasses the 3′-UTR of transcripts from both strands and their polyadenylation sites. PLA2 motifs are present in VP1 N-termini. Some viruses from this genus, e.g. Acheta domestica densovirus, have some VP2 transcripts that are spliced to add a unique, small N-terminal peptide not present in VP1.
Biology
Virus host ranges vary considerably, with some being apparently restricted to a single host while others, such as Junonia coenia densovirus (JcDV, species Lepidopteran ambidensovirus 1), infect many different host species. Ambidensoviruses are typically polytropic in their tissue preferences, multiplying efficiently in most larval, nymph and adult tissues of the host species but not in the midgut.
Species demarcation criteria
Viruses within a species are monophyletic and encode replication initiator proteins (called NS1 or Rep1, 68, or 78) that show >85% amino acid sequence identity.