Genus: Mastrevirus


Genus: Mastrevirus

Distinguishing features

Mastreviruses have a monopartite genome, are leafhopper-transmitted that have only been identified in plants occurring in the Old World (Shepherd et al., 2010). They infect tropical and temperate cereals and some vegetable crops. Many cereal-infecting mastreviruses also infect wild grasses, which are often considered to be the natural hosts of these viruses. This group of geminiviruses utilizes transcript splicing, and therefore their genome contain introns. The proteins translated from the spliced mRNAs encoded by C1 and C2 ORFs are involved in replication and encode the replication initiator protein. In addition, regulation of virion-sense gene expression in some grass-infecting mastreviruses occurs by differential splicing of two virion sense transcripts transcribed from the V1 and V2 ORFs.

Virion

See discussion under family properties.

Genome organization and replication

The mastrevirus genome consists of a single component of circular ssDNA of 2.6–2.8 kb. A small complementary-sense DNA containing 5′-ribonucleotides, annealed within the small intergenic region to the genomic DNA of chloris striate mosaic virus (CSMV), digitaria streak virus (DSV), maize streak virus (MSV), tobacco yellow dwarf virus (TYDV) and wheat dwarf virus (WDV), may be involved in priming complementary-sense DNA synthesis. The small, annealed DNA is subsequently encapsidated with genomic ssDNA.

Mastrevirus genomes encode four proteins (Figure 1.Mastrevirus). The two encoded on the virion-sense strand are the coat protein (CP, gene V1) that encapsidates the virion-sense ssDNA and acts as a nuclear shuttle protein (NSP) for viral DNA, and the movement protein (MP, gene V2), that functions in cell-to-cell movement. The CP appears to regulate the balance of ssDNA and dsDNA accumulation. Regulation of virion-sense gene expression in MSV and grass-infecting relatives occurs by differential transcript splicing. The complementary-sense strand encodes the replication-associated protein (Rep), expressed from genes C1 and C2 by transcript splicing. The Rep protein initiates rolling circle replication by introducing a nick into the conserved TAATATTAC sequence in the virion-sense strand. Rep binds to the large subunit of the replication factor C clamp loader complex, suggesting a role in the recruitment of host replication factors to the origin of replication. The RepA protein (ORF C1), also encoded on the complemetary-sense strand, binds to the plant homologue of retinoblastoma protein (Rb) to regulate cell-cycle progression, altering the environment of terminally differentiated cells to provide host factors that support viral DNA replication. Both Rep and RepA bind to the origin of replication as multimeric proteins. 

Figure 1.Mastrevirus. Genomic organization of mastreviruses. ORFs are denoted as being encoded on the virion-sense (V) or complementary-sense (C) strand, and corresponding protein products are indicated. The positions of the stem-loop motif containing the conserved TAATATTAC sequence in the large intergenic region (LIR) and the encapsidated complementary-sense primer-like molecule (small arrow) in the small intergenic region (SIR) are shown. Introns (open boxes) occur in ORF V2 of some mastreviruses and at the overlap between ORFs C1 and C2 of all mastreviruses. CP, coat protein; MP, movement protein; Rep, replication-associated protein.

The genome contains two intergenic regions. The long intergenic region (LIR) is the location of both the v-ori and transcription start sites, while the short intergenic region (SIR) is the location of both the complementary-strand replication origin and transcription termination sites.

Antigenicity 

Serological analyses indicate that grass-infecting mastreviruses from the same continent constitute distinct groupings: there is an African streak virus group [MSV, Panicum streak virus (PanSV), sugarcane streak virus (SSV), sugarcane streak Egypt virus (SSEV) and sugarcane streak Reunion virus (SSREV)], an Australasian striate mosaic virus group [Bromus catharticus striate mosaic virus (BCSMV), CSMV and Paspalum striate mosaic virus (PSMV)], and the very distinct Asian Miscanthus streak virus (MiSV) and European WDV. Although DSV originates from Vanuatu, it is most closely related to the African mastreviruses. Grass geminiviruses originating from different continents are antigenically either unrelated or only distantly related. Mastreviruses that infect dicot plants are not antigenically related to those that infect monocotyledonous plants.

Biology

Host range

The host range of mastreviruses is relatively narrow. With the exception of TYDV and chickpea chlorotic dwarf virus (CpCDV), which infect plants in the families Solanaceae and Fabaceae, respectively, the host range of mastreviruses is limited to monocot plant species.

Transmission

Mastreviruses are transmitted by specific leafhoppers (order Hemiptera, family Cicadellidae), in most cases by a single species. In common with all geminiviruses, transmission is persistent, circulative and non-propagative. Mastreviruses are normally not transmissible by mechanical inoculation, although MSV has been transmitted experimentally via a vascular puncture technique using maize seeds. Most members are transmitted experimentally to plants by Agrobacterium-mediated transfer (agroinoculation) from partially or tandemly repeated cloned genomic DNA.

Species demarcation criteria

The following criteria are used as a guideline to establish taxonomic status:

  • Nucleotide sequence identity: isolates with a full-length nucleotide sequence identity of  <78% compared to the isolates of any recognized species are considered to belong to a distinct species. This primary criterion can be applied in the absence of additional data, as long as sequence identities are calculated using true pairwise alignments with pairwise deletion of gaps. Nonetheless, when approaching the cut-off value, the biological properties of the virus should also be taken into account.
  • Trans-replication of genomic components: the inability of a Rep protein of one virus to trans-replicate the genomic component of another virus suggests the two viruses should be considered members of different species.
  • Coat protein: members of different species may display serological differences.
  • Different vector species: viruses that are not transmissible by the same insect species may be considered to be belong to different species.
  • Natural host range and symptom phenotype: these characteristics may differ between members of different species, but their commonest use will be to distinguish between the strains of individual species.

A strain demarcation threshold has been established by the Geminiviridae Study Group at <94% shared nt identity of full length nucleotide sequences.

Member Species

SpeciesVirus name(s)Exemplar isolateExemplar accession numberExemplar RefSeq numberAvailable sequenceOther isolatesOther isolate accession numbersVirus Abbreviation(s)Isolate Abbreviation
Axonopus compressus streak virusAxonopus compressus streak virusNigeria/g84/oba/2007KJ437671NC_023864Complete genomeACSV
Bromus catharticus striate mosaic virusBromus catharticus striate mosaic virusAustralia/Queensland/1999HQ113104NC_014822Complete genomeBCSMV
Chickpea chlorosis Australia viruschickpea chlorosis Australia virusAustralia/2614/2010]JN989422NC_022131Complete genomeCpCAV
Chickpea chlorosis viruschickpea chlorosis virusAustralia/3455C/2002/AGU256530NC_014740Complete genomeCpCV/A
Chickpea chlorosis viruschickpea chlorosis virusAustralia/Queensland 21/2003/BGU256531CpCV/B
Chickpea chlorosis viruschickpea chlorosis virusAustralia/3494Ia/2002/CJN989416CpCV/C
Chickpea chlorosis viruschickpea chlorosis virusAustralia/3460B/2002/EJN989426CpCV/E
Chickpea chlorotic dwarf viruschickpea chlorotic dwarf virusSouth Africa/Mpumalanga/1994/BY11023NC_003493Complete genomeCpCDV/B
Chickpea chlorotic dwarf viruschickpea chlorotic dwarf virusSyria/SYR2/2008/AFR687959CpCDV/A
Chickpea chlorotic dwarf viruschickpea chlorotic dwarf virusPakistan/Faisalabad 6/2006/CAM849097CpCDV/C
Chickpea chlorotic dwarf viruschickpea chlorotic dwarf virusPakistan/BGR/2008/DFR687960CpCDV/D
Chickpea chlorotic dwarf viruschickpea chlorotic dwarf virusSudan/Abu Haraz/Nhe/1997/EAM933135CpCDV/E
Chickpea redleaf viruschickpea redleaf virusAustralia/Queensland 22/2003GU256532NC_014739Complete genomeCpRLV
Chickpea yellow dwarf viruschickpea yellow dwarf virusPakistan/PK37/KM377674NC_025475Complete genomeCpYDV
Chickpea yellows viruschickpea yellows virusAustralia/3489B/2002JN989439Complete genomeCpYV
Chloris striate mosaic virusChloris striate mosaic virusAustralia/Queensland/1998M20021NC_001466Complete genomeCSMV
Digitaria ciliaris striate mosaic virusDigitaria ciliaris striate mosaic virusAustralia/Corinda/QG5/2011/BJQ948088NC_018579Complete genomeDCSMV/B
Digitaria ciliaris striate mosaic virusDigitaria ciliaris striate mosaic virusAustralia/Corinda/QG8/2011/AJQ948091DCSMV/A
Digitaria didactyla striate mosaic virusDigitaria didactyla striate mosaic virusAustralia/Queensland/1999HM122238NC_014547Complete genomeDDSMV
Digitaria streak virusDigitaria streak virusVanuatuM23022NC_001478Complete genomeDSV
Dragonfly-associated mastrevirusdragonfly-associated mastrevirus virusPuerto Rico/NZ50/2009JX458740Complete genomeDfasMV
Eragrostis minor streak virusEragrostis minor streak virusNamibia/Caprivi/g450/2009JF508490NC_015553Complete genomeEMSV
Eragrostis streak virusEragrostis streak virusZimbabwe/Guruwe 186/2007EU244915NC_010352Complete genomeESV
Maize streak Reunion virusmaize streak Reunion virusLa Reunion/St Pierre/PR52/2009JQ624879NC_017917Complete genomeMSRV
Maize streak virusmaize streak virusSouth Africa/AY00514NC_001346Complete genomeMSV/A
Maize streak virusmaize streak virusSouth Africa/Worester/Plaas Staal B/g27b/2006/BEU628597MSV/B
Maize streak virusmaize streak virusSouth Africa/Mt Edgecomb/Setaria/1988/CAF007881MSV/C
Maize streak virusmaize streak virusSouth Africa/Rawsonville/1998/DAF329889MSV/D
Maize streak virusmaize streak virusSouth Africa/Mitchelle Park/Natal A/g125/Dig/2006/EEU628626MSV/E
Maize streak virusmaize streak virusNigeria/IITA B/g88/Urochloa/2007/FEU628629MSV/F
Maize streak virusmaize streak virusMali/Mic25/Digitaria/1987/GEU628631MSV/G
Maize streak virusmaize streak virusNigeria/Lagbaka/g79/Setaria/2007/HEU628638MSV/H
Maize streak virusmaize streak virusSouth Africa/New Germany/Natal/A/g217/Digitaria/2007/IEU628639MSV/I
Maize streak virusmaize streak virusZimbabwe/Mic24K/Pennisetum/1987/JEU628641MSV/J
Maize streak virusmaize streak virusUganda/Busia 4/Eustachys/2005/KEU628643MSV/K
Miscanthus streak virusMiscanthus streak virusJapan/1991D01030NC_003379Complete genomeMiSV
Oat dwarf virusoat dwarf virusGermany/Saxena 25/2006AM296025NC_010799Complete genomeODV
Panicum streak virusPanicum streak virusSouth Africa/Karino/1989/AL39638NC_001647Complete genomePanSV/A
Panicum streak virusPanicum streak virusKenya/1990/BX60168PanSV/B
Panicum streak virusPanicum streak virusZimbabwe/Guruwe 169/Urochloa/2006/CEU224264PanSV/C
Panicum streak virusPanicum streak virusNigeria/Ifon 91/Urochloa/2007/DEU224265PanSV/D
Panicum streak virusPanicum streak virusKenya/Jic10/1997/EGQ415391PanSV/E
Panicum streak virusPanicum streak virusKenya/Nye2/g364/2008/FGQ415392PanSV/F
Panicum streak virusPanicum streak virusMayotte/Cac/g385/2008/GGQ415395PanSV/G
Panicum streak virusPanicum streak virusCentral African Republic/Bai2/Car11/Brachiaria/2008/HGQ415397PanSV/H
Panicum streak virusPanicum streak virusKenya/Nra1/g374/2008GQ415399PanSV/I
Paspalum dilatatum striate mosaic virusPaspalum dilatatum striate mosaic virusAustralia/Landsborough/QG46/2011JQ948061NC_018576Complete genomePDSMV
Paspalum striate mosaic virusPaspalum striate mosaic virusAustralia/Queensland/1611/2003/AJF905486NC_018530Complete genomePSMV/A
Paspalum striate mosaic virusPaspalum striate mosaic virusAustralia/Farrant Hill/3011/2011/BJQ948069PSMV/B
Saccharum streak virusSaccharum streak virusSouth Africa/Empageni/T1/2008GQ273988NC_013464Complete genomeSacSV
Sporobolus striate mosaic virus 1Sporolobus striate mosaic virus 1Australia/Wyaga/3020_1/2011JQ948051NC_018577Complete genomeSSMV1
Sporobolus striate mosaic virus 2Sporolobus striate mosaic virus 2Australia/Wyaga/3020_2/2011JQ948052NC_018578Complete genomeSSMV2
Sugarcane chlorotic streak virussugarcane chlorotic streak virusNigeria/Sc-10/SR/1/2015KX787914NC_032004Complete genomeSCSV
Sugarcane streak Egypt virussugarcane streak Egypt virusEgypt/AswanAF037752NC_001868Complete genomeSSEV
Sugarcane streak Reunion virussugarcane streak Reunion virusReunion/R574/AAF072672NC_004755Complete genomeSSREV/A
Sugarcane streak Reunion virussugarcane streak Reunion virusZimbabwe/Nyangombe 177/Paspalum/2006EU244916SSREV/B
Sugarcane streak virussugarcane streak virusSouth Africa/Natal/AM82918NC_003744Complete genomeSSV/A
Sugarcane streak virussugarcane streak virusLa Reunion/St Pierre/Pie/R5/Cenchrus/2006/BEU244914SSV/B
Sugarcane striate virussugarcane striate virusChina/WZG/2014KR150789Complete genomeSStrV
Sugarcane white streak virusSugarcane white streak virusSudan/VARX/2013KJ210622NC_023989Complete genomeSWSA/A
Sweet potato symptomless virus 1sweet potato symptomless virus 1Kenya/Q44429/2005KY565231Complete genomeSpSV/1
Switchgrass mosaic-associated virusswitchgrass mosaic-associated virusUnited States/DB/2012KF806701NC_025834Complete genomeSgMaV
Tobacco yellow dwarf virustobacco yellow dwarf virusAustralia/1992M81103NC_003822Complete genomeTbYDV
Urochloa streak virusUrochloa streak virusNigeria/Ipetumodu/g226/2007EU445699NC_010797Complete genomeUSV
Wheat dwarf India viruswheat dwarf India virusIndia/2010JQ361910NC_017828Complete genomeWDIV
Wheat dwarf viruswheat dwarf virusTurkey/barley/AAJ783960Complete genomeWDV/A
Wheat dwarf viruswheat dwarf virusIran/2008/BFJ620684WDV/B
Wheat dwarf viruswheat dwarf virusHungary/Kompolt10/1/2010/CJQ647455WDV/C
Wheat dwarf viruswheat dwarf virusIran/Bavanat/2010/DJN791096WDV/D
Wheat dwarf viruswheat dwarf virusHungary/B/2005/EAM040732WDV/E

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