Genus: Comovirus

Genus: Comovirus

Distinguishing features

Comoviruses have bipartite genomes encapsidated by two capsid proteins (CP); these viruses are transmitted by beetles.

Virion

The comovirus capsid is made of two types of polypeptides (large CP: 40–45 kDa and small CP: 21–27 kDa). The small CP suppresses RNA silencing and surface-exposed amino acids are required for this function.

Genome organisation and replication

The 5ʹ- and 3ʹ-UTRs of RNA-1 and RNA-2 are similar in sequence but not identical. RNA-2 is translated into two largely overlapping polyproteins that are processed into three domains. Production of the smaller polyprotein results from internal initiation at a downstream AUG, which is placed in a more favourable context than the upstream AUG (Figure 1.Comovirus). The 58K protein released from the N-terminus of the larger polyprotein (P2) is necessary for replication of RNA-2. The 48K protein released from the N-terminus of the smaller polyprotein (P2ʹ) is the movement protein (MP), with a typical “LPL” motif. The CP domains are encoded at the C-terminus of both polyproteins. The MP and the CPs are required for cell-to-cell movement of the virus (Wellink and Van Kammen 1989). The MP is a structural component of tubular structures containing virus-like particles that traverse the cell wall. The C-terminal region of the MP also interacts with the large CP (Carvalho et al., 2003). RNA-1 is translated into a single polyprotein that is processed into five domains, through alternative processing pathways (Figure 1.Comovirus). The N-terminal 32K protein limits the processing of the RNA-1-encoded polyprotein in cis and assists the processing of the RNA-2-encoded polyprotein (Peters et al., 1992). This protein is often referred to as the protease co-factor or Co-Pro. The replication block on the RNA-1-encoded polyprotein includes the 58K protein with sequence motifs characteristic of an NTP-binding helicase, the VPg, the Pro and the Pol. The 32K Co-Pro and 58K NTB proteins are involved in inducing the cytopathic structure through proliferation of ER-derived membranes (Carette et al., 2002).

Figure 1.Comovirus. Genome organization and polyprotein processing of cowpea mosaic virus. The ORFs are boxed and the function of the proteins is indicated. MP: movement protein; CPL and CPS: large and small capsis proteins; Co-Pro: proteinase co-factor; NTB: NTP-binding proteins; Pro: proteinase; Pol: RNA-dependent RNA polymerase. Proteolytic cleavage sites are indicated on the polyproteins with the vertical lines. All intermediate and final cleavage products have been detected in infected cells. The black circles at the 5′-end of the RNA represents the VPg, and A(n) at the 3′-end the poly-A tail.

Biology

Comoviruses have narrow host ranges, 11 of the 15 species being restricted to a few species of the family Leguminosae. Mosaic and mottle symptoms are characteristic, but usually not ringspots. Transmission in nature is exclusively by beetles, especially members of the family Chrysomelidae. Beetles retain their ability to transmit virus for days or weeks.

Species demarcation criteria

See discussion under family description.

Member species

Exemplar isolate of the species
SpeciesVirus nameIsolateAccession numberRefSeq numberAvailable sequenceVirus Abbrev.
Andean potato mottle virusAndean potato mottle virusCL16239NC_038744Partial genomeAPMoV
Bean pod mottle virusbean pod mottle virusKY/G/7RNA-1: M62738;
RNA-2: U70866
All
RNA-1: NC_003495;
RNA-2: NC_003496
All
Complete genomeBPMV
Bean rugose mosaic virusbean rugose mosaic virusParanaRNA-1: KP404602;
RNA-2: KP404603
All
RNA-1: NC_028139;
RNA-2: NC_028146
All
Complete genomeBRMV
Broad bean stain virusbroad bean stain virus7013RNA-1: KJ746622;
RNA-2: FJ028650
All
RNA-1: NC_043386;
RNA-2: NC_043385
All
Partial genomeBBSV
Broad bean true mosaic virusbroad bean true mosaic virusEV-11RNA-1: GU810903;
RNA-2: GU810904
All
RNA-1: NC_022004;
RNA-2: NC_022006
All
Complete genomeBBTMV
Comovirus ArLV1Arabidopsis latent virus 1MH899120;
MH899121
All
Complete genomeArLV1
Comovirus PepMMVpepper mild mosaic virusMK990555;
MK990556
All
Complete genomePepMMV
Comovirus PvSMVPhaseolus vulgaris severe mosaic virusMN837498;
MN837499
All
Complete genomePvSMV
Cowpea mosaic viruscowpea mosaic virusvan WezenbeekRNA-1: X00206;
RNA-2: X00729
All
RNA-1: NC_003549;
RNA-2: NC_003550
All
Complete genomeCPMV
Cowpea severe mosaic viruscowpea severe mosaic virusChenRNA-1: M83830;
RNA-2: M83309
All
RNA-1: NC_003545;
RNA-2: NC_003544
All
Complete genomeCPSMV
Glycine mosaic virusGlycine mosaic virusNo entry in GenbankGMV
Pea green mottle viruspea green mottle virusNo entry in GenbankPGMV
Pea mild mosaic viruspea mild mosaic virusNo entry in GenbankPMiMV
Quail pea mosaic virusquail pea mosaic virusNo entry in GenbankQPMV
Radish mosaic virusradish mosaic virusJapaneseRNA-1: AB295643;
RNA-2: AB295644
All
RNA-1: NC_010709;
RNA-2: NC_010710
All
Complete genomeRaMV
Red clover mottle virusred clover mottle virusSRNA-1: X64886;
RNA-2: M14913
All
RNA-1: NC_003741;
RNA-2: NC_003738
All
Complete genomeRCMV
Squash mosaic virussquash mosaic virusYRNA-1: AB054688;
RNA-2: AB054689
All
RNA-1: NC_003799;
RNA-2: NC_003800
All
Complete genomeSqMV
Ullucus virus CUllucus virus CNo entry in GenbankUVC

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

Related, unclassified viruses 

Virus name

Accession number

Virus abbreviation

turnip ringspot virus

RNA-1: FJ516745; RNA-2: FJ516746

TuRSV

Virus names and virus abbreviations are not official ICTV designations.

Turnip ringspot virus (TuRSV) is related to radish mosaic virus (RaMV). They infect similar hosts. The degree of aa sequence identity between the two viruses is close to the proposed species demarcation criteria (73% aa sequence identity in the combined CP region and 80% aa sequence identity in the Pro-Pol region) (Petrzik and Koloniuk 2010). It is not known whether re-assortment between the RNAs of TuRSV and RaMV is possible. Therefore, the taxonomic position of TuRSV as a distinct species in the genus Comovirus or as a distant strain of the species Radish mosaic virus remains unclear.