ICTV Virus Taxonomy Profile: Partitiviridae

1Virus particles are isometric, non-enveloped, and 25–43 nm in diameter (Table 1, Fig. 1a, b). Each capsid is composed of 120 copies of a single protein arranged as 60 dimers with T=1 icosahedral symmetry. Dimeric surface protrusions are frequently observed on viral capsids. One or two molecules of RNA-dependent RNA polymerase (RdRP) are packaged inside each particle.

2Each dsRNA is monocistronic. The RdRP is believed to function as both a transcriptase and a replicase and catalyzes in vitro end-to-end transcription of each dsRNA to produce mRNA by a semi-conservative mechanism. Virions accumulate in the cytoplasm.

3Members of all five genera possess two essential genome segments, dsRNA1 and dsRNA2, each containing one large ORF on the positive-strand RNA molecule (Fig. 2). The smaller of the two dsRNA genome segments usually encodes the coat protein (CP) and the larger usually encodes the virion-associated RNA polymerase. The linear dsRNA segments are separately encapsidated. Additional dsRNA segments (satellite or defective) may also be present.

4Members of the genus Alphapartitivirus infect either plants, or ascomycetous or basidiomycetous fungi. The two essential dsRNA genome segments are individually about 1.9–2.0 kbp (dsRNA1) and 1.7–1.9 kbp (dsRNA2), typically containing a poly(A) tract near the plus-strand 3′-terminus. There is a single major CP with predicted Mr of 51–57 kDa. Plant alphapartitiviruses cause persistent infections, whereas some fungal alphapartitiviruses cause host effects, such as hypovirulence or a reduced growth rate.

5Members of the genus Betapartitivirus infect either plants, or ascomycetous or basidiomycetous fungi. The two essential dsRNA genome segments are about 2.2–2.4 kbp (dsRNA1) and 2.1–2.4 kbp (dsRNA2), typically containing a poly(A) tract near the plus-strand 3′-terminus. There is a single major CP with predicted Mr of 71–77 kDa. Plant betapartitiviruses cause persistent infections. Some fungal betapartitiviruses cause reduced host virulence and changes in colony morphology.

6All known members of the genus Gammapartitivirus infect ascomycetous fungi. The two essential dsRNA segments are about 1.6–1.8 kbp (dsRNA1) and 1.4–1.6 kbp (dsRNA2). There is a single major CP with predicted Mr of 44–47 kDa. Most gammapartitiviruses seem to induce latent infections. Aspergillus fumigatus partitivirus 1, a related, unclassified virus, has been associated with host effects.

7All known members of the genus Deltapartitivirus induce persistent infections in plants. They are transmitted by ovule and pollen to the seed embryo. The two essential dsRNA segments are individually 1.6–1.7 kbp (dsRNA1) and 1.4–1.6 kbp (dsRNA2). There is a single major CP with predicted Mr of 38–49 kDa.

8Members of the genus Cryspovirus infect apicomplexan protozoa of the genus Cryptosporidium. The viral genome comprises two dsRNA segments, which are individually 1.5 and 1.8 kbp. There is a single major CP with predicted Mr of 37 kDa. Virions are disseminated within Cryptosporidium oocysts. Infections of the Cryptosporidium host cells appear to be latent.

9Full ICTV Online (10th) Report: www.ictv.global/report/partitiviridae.