Genus: Bromovirus


Genus: Bromovirus

Distinguishing features

Beetle vectors are recorded for most bromoviruses but the efficiency of such transmission is low. A long-standing report of transmission by nematodes has yet to be confirmed.

Virion

Morphology

Virions are polyhedral, and all the same size, with a diameter of 27 nm.

Physicochemical and physical properties

Virions prepared below pH 6.0 have S20,w of 88S, are stable to high salt and low detergent concentrations, and are nuclease- and protease-resistant. At pH 7.0 and above, virions swell to a diameter of 31 nm, S20,w decreases to 78S, salt and detergent stability decreases dramatically, and protein and RNA are susceptible to hydrolytic enzymes. This swelling is accompanied by conformational changes of the capsid that are detectable by physical and serological means.

Nucleic acid

RNA 3′-termini are tRNA-like, are very similar in all viruses sequenced so far, and can be aminoacylated with tyrosine.

Proteins

Virions contain a single coat protein (CP) of 20.3 kDa.

Lipids

Lipids are not associated with virions 

Carbohydrates

Carbohydrates are not associated with virions 

Genome organization and replication 

The genome is organized as depicted in Figure 2A.Bromoviridae. Coat protein is not required for activation of the genome. Intra-segmental crossover as well as homologous recombination may occur in brome mosaic virus (BMV) RNAs. Both, viral RNA sequences and host protein contribute to BMV RNA recombination (Kolondam et al., 2015). Data from NGS revealed that BMV virions can carry host RNAs that potentially can mediate horizontal gene transfer in plants (Shrestha et al., 2018).

Antigenicity

All members are serologically related, with large antigenic differences between species.

Biology 

The natural host range is narrow, and is limited to a few plant hosts for each member of this genus. All members of the species are thought to be beetle-transmitted. BMV is also transmitted by aphids in a non-persistent manner but with poor efficiency.

Species demarcation criteria

Criteria used for demarcation of species within the genus are host range, serological relationships, comparable replicase proteins (i.e. 1a and 2a proteins) and nucleotide sequence identity between species, which ranges from 50 to 80% depending on the gene used for comparison.

Member species

SpeciesVirus name(s)Exemplar isolateExemplar accession numberExemplar RefSeq numberAvailable sequenceOther isolatesOther isolate accession numbersVirus abbreviationIsolate abbreviation
Broad bean mottle virusbroad bean mottle virusDzianottRNA1: M65138; RNA2: M64713; RNA3: M60291RNA1: NC_004008; RNA2: NC_004007; RNA3: NC_004006Complete genomeBBMV
Brome mosaic virusbrome mosaic virusRussian wheatRNA1: X02380; RNA2: X01678; RNA3: J02042RNA1: NC_002026; RNA2: NC_002027; RNA3: NC_002028Complete genomeBMV
Cassia yellow blotch viruscassia yellow blotch virusKU1RNA1: AB194806; RNA2: AB194807; RNA3: AB194808RNA1: NC_006999; RNA2: NC_007000; RNA3: NC_007001Complete genomeCYBV
Cowpea chlorotic mottle viruscowpea chlorotic mottle virusDzianottRNA1: M65139; RNA2: M28817; RNA3: M28818RNA1: NC_003543; RNA2: NC_003541; RNA3: NC_003542Complete genomeCCMV
Melandrium yellow fleck virusmelandrium yellow fleck virusKU1RNA1: AB444583; RNA2: AB444584; RNA3: AB444585RNA1: NC_013266; RNA2: NC_013267; RNA3: NC_013268Complete genomeMYFV
Spring beauty latent virusspring beauty latent virusKU1RNA1: AB080598; RNA2: AB080599; RNA3: AB080600RNA1: NC_004120; RNA2: NC_004121; RNA3: NC_004122Complete genomeSBLV

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

Derivation of names 

Bromo: from the type species Brome mosaic virus