Genus: Ilarvirus


Genus: Ilarvirus

Distinguishing features

Ilarviruses are transmitted mechanically by thrips feeding on pollen grains containing the virus or by carrying pollen grains contaminated by the virus.  The RNA2 of members of subgroups 1 and 2 is bicistronic producing a 2b protein, which for asparagus virus 2 is proven to be a suppressor of post-transcriptional gene silencing (Shimura et al., 2013).

Virion

Morphology

Virions of most members of the genus have quasi-isometric (26–36 nm in diameter) or occasionally bacilliform particles of four different size classes (Figure 1B.Bromoviridae). Bacilliform particles occur in plants infected by prune dwarf virus (PDV), tulare apple mosaic virus (TAMV), prunus necrotic ringspot virus (PNRSV), apple mosaic virus (ApMV) and spinach latent virus (SpLV). Cryoelectron microscopy of preparations of tobacco streak virus (TSV), a member of the type species Tobacco streak virus, revealed isometric particles permeated by numerous pores, which may explain the lability of these viruses (Figure 1E.Bromoviridae) (Pallas et al., 2013). 

Nucleic acid

There is a short region of sequence similarity at the 3′-ends of the RNAs.

Proteins

Virions contain a coat protein (CP) of 24.5 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 for ilarviruses of subgroups 3 and 4 and Figure 2C.Bromoviridae for ilarviruses of subgroups 1 and 2. The CP is required for activation of replication, but may be substituted with CP from alfalfa mosaic virus (genus Alfamovirus).

Antigenicity

Virions are “unpromising subjects for the raising of good antisera” (Bujarski et al., 2012). Subgroups within the genus were defined based on the presence of serological relationships among some, but not all, members of each subgroup. Sequence data have supported many of the serological relationships but also showed potential relationships among viruses not previously demonstrated as related. Some serological relationships have been reported between viruses in different subgroups and might be associated with conserved amino acids and secondary structures. Monoclonal antibodies and antibodies produced against recombinant proteins (Abou-Jawdah et al., 2004, Menzel et al., 2012) have addressed some of the problems associated with the serological detection of ilarviruses (Pallas et al., 2013). 

Biology

Ilarviruses mainly infect woody plants. Viruses are present in/on the pollen and may be transmitted when wind-blown pollen and populations of vector thrips are coincident on a susceptible host.

Species demarcation criteria 

Criteria used for demarcation of species within the genus are serology, host range and sequence similarity although specific levels of sequence similarity have not been defined.

Ilarviruses were initially grouped on the basis of serological relationships. Sequence data have confirmed some of these groupings but have also shown that some species were grouped inappropriately (Pallas et al., 2013).

Member species

SpeciesVirus name(s)Exemplar isolateExemplar accession numberExemplar RefSeq numberAvailable sequenceOther isolatesOther isolate accession numbersVirus abbreviationIsolate abbreviation
Ageratum latent virusAgeratum latent virus 19981998RNA1: JX463340; RNA2: JX463341; RNA3: JX463342RNA1: NC_022127; RNA2: NC_022128; RNA3: NC_022129Complete genomeAGLV
American plum line pattern virusamerican plum line pattern virusScottRNA1: AF235033; RNA2: AF235165; RNA3: AF235166RNA1: NC_003451; RNA2: NC_003452; RNA3: NC_003453Complete genomeAPLPV
Apple mosaic virusapple mosaic virusShielRNA1: AF174584; RNA2: AF174585; RNA3: U15608RNA1: NC_003464; RNA2: NC_003465; RNA3: NC_003480Complete genomeAMV
Asparagus virus 2asparagus virus 2USARNA1: EU919666; RNA2: EU919667; RNA3: X86352RNA1: NC_011808; RNA2: NC_011809; RNA3: NC_011807Complete genomeAV2
Blackberry chlorotic ringspot virusblackberry chlorotic ringspot virusUKRNA1: DQ091193; RNA2: DQ091194; RNA3: DQ091195RNA1: NC_011553; RNA2: NC_011554; RNA3: NC_011555Complete genomeBCRV
Blueberry shock virusblueberry shock virusBerkelyRNA1: KF031037; RNA2: KF031038; RNA3: KF031039RNA1: NC_022250; RNA2: NC_022251; RNA3: NC_022252Complete genomeBSV
Citrus leaf rugose viruscitrus leaf rugose virusScottRNA1: U23715; RNA2: U17726; RNA3: U17390RNA1: NC_003548; RNA2: NC_003547; RNA3: NC_003546Complete genomeCLRV
Citrus variegation viruscitrus variegation virusLiRNA1: EF584664; RNA2: EF584665; RNA3: U17389RNA1: NC_009537; RNA2: NC_009538; RNA3: NC_009536Complete genomeCVV
Elm mottle viruselm mottle virusScottRNA1: U57047; RNA2: U34050; RNA3: U85399RNA1: NC_003569; RNA2: NC_003568; RNA3: NC_003570Complete genomeEMoV
Fragaria chiloensis latent virusFragaria chiloensis latent virusCFRA 9087RNA1: AY682102; RNA2: AY707771; RNA3: AY707772RNA1: NC_006566; RNA2: NC_006567; RNA3: NC_006568Complete genomeFCILV
Humulus japonicus latent virusHumulus japonicus latent virusUKRNA1: AY500236; RNA2: AY500237; RNA3: AY500238RNA1: NC_006064; RNA2: NC_006065; RNA3: NC_006066Complete genomeHJLV
Lilac leaf chlorosis viruslilac leaf chlorosis virusVargaRNA1: HE572565; RNA2: FN669168; RNA3: FN669169RNA1: NC_025477; RNA2: NC_025478; RNA3: NC_025481Complete genomeLLCV
Lilac ring mottle viruslilac ring mottle virusNetherlandsRNA2: EU919669; RNA3: U17391RNA2: NC_038777; RNA3: NC_038776Partial genomeLRMV
Parietaria mottle virusparietaria mottle virusGeRNA1: AY496068; RNA2: AY496069; RNA3: U35145RNA1: NC_005848; RNA2: NC_005849; RNA3: NC_005854Complete genomePMV
Privet ringspot virusprivet ringspot virusWin-01RNA1: KT290039; RNA2: KT290040; RNA3: KT290041RNA1: NC_027928; RNA2: NC_027929; RNA3: NC_027930Complete genomePrRSV
Prune dwarf virusprune dwarf virusSalmo BC cherryRNA1: U57648; RNA2: AF277662; RNA3: L28145RNA1: NC_008039; RNA2: NC_008037; RNA3: NC_008038Complete genomePDV
Prunus necrotic ringspot virusprunus necrotic ringspot virusCH57RNA1: AF278534; RNA2: AF278535; RNA3: U57046RNA1: NC_004362; RNA2: NC_004363; RNA3: NC_004364Complete genomePNRV
Spinach latent virusspinach latent virusScottRNA1: U93192; RNA2: U93193; RNA3: U93194RNA1: NC_003808; RNA2: NC_003809; RNA3: NC_003810Complete genomeSLV
Strawberry necrotic shock virusstrawberry necrotic shock virusMarylandRNA1: DQ318818; RNA2: AY743591; RNA3: AY363228RNA1: NC_008708; RNA2: NC_008707; RNA3: NC_008706Complete genomeSNSV
Tobacco streak virustobacco streak virusWCRNA1: U80934; RNA2: U75538; RNA3: X00435RNA1: NC_003844; RNA2: NC_003842; RNA3: NC_003845Complete genomeTSV
Tomato necrotic streak virustomato necrotic streak virus13-382RNA1: KT779204; RNA2: KT779205; RNA3: KT779206RNA1: NC_039074; RNA2: NC_039075; RNA3: NC_039076Complete genomeTomNSV
Tulare apple mosaic virustulare apple mosaic virusScottRNA1: AF226160; RNA2: AF226161; RNA3: AF226162RNA1: NC_003833; RNA2: NC_003834; RNA3: NC_003835Complete genomeTAMV

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

Derivation of names

Ilar: from isometric labile ringspot

Related, unclassified viruses

Virus name

Accession number

Virus abbreviation

Subgroup 1

Bacopa chlorosis virus

RNA1: FJ607140; RNA2: FJ607141; RNA3: FJ607142

(BaCV)

tomato necrotic spot virus

RNA3: FJ236810

(ToNSV)

cape gooseberry ilarvirus 1

RNA1: MG201991; RNA2: MG201992; RNA3: MG201993

(CGIV-1)

Subgroup 3

apple necrotic mosaic virus

RNA1: KI808376; RNA2: KI808377; RNA3: KI808378

(ApNMV)

Subgroup 4

Viola white distortion virus

RNA3: GU168941

(VWDV)

Virus names and virus abbreviations are not official ICTV designations.