Family: Alphaflexiviridae
Genus: Platypuvirus
Distinguishing features
This genus includes a single species, Donkey orchid symptomless virus, whose members infect native Australian orchids. The virus genome is predicted to encode seven proteins of apparently disparate origins. The replication-associated protein (Rep) and capsid protein (CP) are related to viruses of the family Alphaflexiviridae, whereas the movement protein (MP) shares an evolutionary history with the MP of dianthoviruses. Other putative proteins are distant from any other plant virus proteins (Wylie et al., 2013, Wylie et al., 2013).
Virion
Morphology
No information.
Physicochemical and physical properties
No information.
Nucleic acid
Donkey orchid symptomless virus (DOSV) virions are presumed to contain a single molecule of linear single-stranded RNA of 7838 nt, excluding the 3′-poly(A) tail (Figure 1. Platypuvirus).
Proteins
The only structural protein is the CP, composed of 202 aa (22 kDa).
Carbohydrates
None reported.
Genome organization and replication
The genomic RNA is predicted to encode seven proteins of apparently disparate origins (Figure 1. Platypuvirus). A 69 kDa protein (ORF1) that overlaps the Rep shares low identity with MPs of tymoviruses (Tymoviridae). A 157 kDa Rep (ORF2) and 22 kDa capsid protein (ORF4) share 32% and 40% amino acid identity, respectively, with homologous proteins encoded by members of the family Alphaflexiviridae. A 44-kDa protein (ORF3) shares low identity with myosin and an autophagy protein from squirrelpox virus. A 27 kDa protein (ORF5) shares no identity with any described protein. A 14 kDa protein (ORF6) shares low sequence identity (26%) over a limited region with the envelope glycoprotein precursor of Crimea-Congo hemorrhagic fever virus (Bunyaviridae) which infects mammals. The putative 25 kDa movement protein (MP) (ORF7) shares limited (27%) identity with 3A-like MPs of members of the families Tombusviridae and Virgaviridae.
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Figure 1. Platypuvirus. Donkey orchid symptomless virus genome organization showing the relative positions of the ORFs and their expression products. Mtr, methyltransferase; Hel, helicase; RdRP, RNA-directed RNA polymerase; CP, capsid protein. |
Biology
Members of the only species of this genus have been found infecting native Australian orchids and can be mechanically transmitted to Nicotiana benthamiana.
Derivation of names
Platypuvirus: from platypus because it appears to combine features of different virus lineages, in the same way that the platypus (Ornithorhynchus anatinus) combines features of different vertebrate lineages.
Species demarcation criteria
Since there is currently only a single species in the genus, species demarcation criteria are not currently defined, but following criteria for other genera in the family, different species should have less than 72% nt identity (or 80% aa identity) between their respective CP or Rep genes, although biological properties should also be considered.