Genus: Rymovirus

Genus: Rymovirus

Distinguishing features

This genus includes three species. Rymoviruses are presumably transmitted by host-adapted populations of eriophyid mite species in a semi-persistent manner. Rymoviruses share a reciprocal monophyletic relationship with members of the genus Potyvirus (French and Stenger 2005).

Virion

Morphology

Virions are flexuous filaments 690–720 nm×11–15 nm in size.

Physicochemical and physical properties

Virion density in CsCl is 1.325 g cm-3 (for ryegrass mosaic virus (RGMV). Virion Sedimentation coefficient S20,w is 165–166S for most members.

Nucleic acid

Virions contain a single molecule of linear positive-sense ssRNA of about 9.5 kb with a 3′-poly(A) terminus.

Proteins

Rymoviruses encode one type of CP, with a theoretical Mr of 35,482 Da and an apparent Mr estimated by Western blots of 45 kDa for RGMV.

Genome organization and replication

The complete genome sequences available for isolates of RGMV, Agropyron mosaic virus (AgMV), and Hordeum mosaic virus (HoMV), indicate that rymoviruses have a genome organization (Figure1.Rymovirus) and replication strategy similar to other members of the Potyviridae with monopartite genomes (Figure 2.Potyviridae).

Figure 1.Rymovirus Schematic diagram of the ryegrass mosaic virus (RMV) genome. The polyprotein ORF is indicated by the large open box divided into putative mature proteins. The pretty interesting Potyviridae protein (PIPO) is represented by a small box. The untranslated regions (UTR) are represented by lines on each end of the large ORF. Activities of mature proteins are postulated by analogy with genus Potyvirus. Conventions are as for the potyvirus genome organization map (Figure 2.Potyviridae). Not to scale.

Biology

Host range

Most rymoviruses have limited, but widespread host ranges within the family Poaceae, whereas some have relatively narrow host ranges.

Transmission

Transmission by eriophyid mites and mechanical transmission have been reported for most members. The eriophyid mites transmitting rymoviruses are different from those transmitting tritimoviruses. The cereal rust mite Abacarus hystrix transmits both RGMV and AgMV, but only the former is efficiently transmitted. No vector is known for HoMV. Recent studies have revealed that host-associated populations of A. hystrix represent a species complex.

Antigenicity

Particles of most rymoviruses are moderately immunogenic. HoMV and AgMV are serologically related.

Species demarcation criteria

See discussion under family description.

Member species

Exemplar isolate of the species
SpeciesVirus nameIsolateAccession numberRefSeq numberAvailable sequenceVirus Abbrev.
Agropyron mosaic virusAgropyron mosaic virusND402AY623626NC_005903Complete genomeAgMV
Hordeum mosaic virusHordeum mosaic virusATCC PV81AY623627NC_005904Complete genomeHoMV
Ryegrass mosaic virusryegrass mosaic virusDanishY09854NC_001814Complete genomeRGMV

Virus names, the choice of exemplar isolates, and virus abbreviations are not official ICTV designations.