FAMILY NANOVIRIDAE

Nanoviridae

Taxonomie strueture of the familyFamily NanoviridaeGenus NanovirusGenus Babllvirlls

Distinguishing featuresThe family Nanoviridae comprises plant viruses possessing very small virions containing a multi­partite «(Hl), eireular, single stranded DNA genome and being lransmitted by aphids in a circula­tive (non-propagative) persistent manner. Eaeh virion contains one eomponent of the multipartitegenome and 60 subunits of a eapsid protein (Cr) of about19kDa.

Virion properties

MORPHOLOGY

Virions are 17-20nm in diameter, and presumably of an ieosahedral T = 1 symmetry strueture eon­taining 60 subunits. They are not enveloped. Capsomeres may be evident, produeing an angular orhexagonal outline (Figure 1).

PHYSICOCHEMICAL AND PHYSICAL PROPERTIESVirions are stable in Cs,Sü, but may not be stable in CsCI. The buoyant density of virions is about1.24 to 1.30gem-3 in Cs,Sü" and 1.34gem-3 in CsCI. They sediment as a single eomponent insuerose rate-zonal and Cs,Sü, isopyenie density gradients. The sedimentation eoeffieient of bananabunehy top virus (BBTV) virions is 465. The particle weight of subterranean clover stunt virus(5C5V) is approximately 1.6 X 106 The extinetion eoeffieient of 5C5V is 3.6 at A2f,(J (eorreeted forlight scattering).

NUCLEIC ACID5ix er eight eireular single stranded (ss)ONAs ranging in size from 923 to 1111 nucleotides (nt) areeonsistently found in virion preparations of different babu- and nanovirus isolates. They are eneap­sidated as individual positive sense strands in separate particles. In addition, up to four differentsatellite-like 550 As of about100ü-nOOnt, also referred to as alphasatellites, are found assoeiatedwith the majority of the nanovirid isolates.

PROTElNSVirions have a single cr of about19kDa. No other proteins have been found assoeiated with viri­ons. In addition, at least 5-7 non-struetural proteins are eneoded by the mRNA(s) transeribed fromthe nanovirid ssONAs (Table 1). All but one of the nanovirid DNAs eneode only a single protein.

Figure 1: Negative contrast electron micrograph of particles of Faba bean necrotic yellows virus (FBNYV). The bar repre­senls 50nm. (Courtesy of L. Katul and D.-E. Lesemann.)

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Virus Tnonomy: Ninth Report of Ihe Inlern.llional Committee on Taxonomy vf Viru~sCl 20121nlernational Commiuee on Taxonomy of Viruses. Published by EIs.tl\'ier [ne. All Rights Rest!fVed. 395

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A second virion-sense ORF, eomplete!y nested within the M-Rep-eneoding ORF and encodinga putative 5 kDa protein 01 unknown funetion (U5), was identified only Irom banana bunehy topvirus (BBTV) 0 A-R but not lrom any other nano- and babuvirus DNA-R.

LIPIDSNot known.

CARBOHYDRATESNot known.

Genome organization and replicationBased on a range 01 geographical isolates, there is eompelling evidenee that 6 and 8 0 As are essen­tial and lorm the genome 01 a babu- and nanovirus, respeetively (Figures 2 and 3). All nanoviridDNAs have a similar structural organization, containing conserved inverted repeat sequences poten­tially lorming a stem-Ioop strueture that is part 01 the eomrnon region-stern loop [CR-5LJ, and a see­ond eommon region named CR-M (Ior babuviruses) or CR-lI (Ior nanoviruses) (Figures 2 and 3).The additional satellite-like DNAs eontain different inverted repeat sequences (stern loops).

Babu- and nanoviruses share a set 01 live homologous DNA eomponents, relerred to as DNA-R, -5,-C, -M and -N (Figures 2 and 3). Three other DNAs (DNA-Ul, -U2 and -U4) eneoding proteins 01as yet unknown lunetions have been identified from nanoviruses only and one lurther DNA(DNA-U3) only lrom babuviruses. It should be noted, however, that no ORF has been identifiedfrom the DNA-U3 01 the two Abaea bunehy top virus (ABTV) isolates and several Asian iso!ates 01BBTY. Whereas the differenee in the number and types 01 0 As between babu- and nanovirusesrefleets a fundamental dillerenee between viruses 01 these two genera, the apparent disparity ingenomic organizations between same viruses of a genus may indicate that certain genome com­ponents have not yet been identified. This might be true for DNA-U2 and -U4 of 5C5V and seemsdefinitely to be the case lor cardamom bushy dwarl virus (CBDV) DNAs other than DNA-R.

All nanovirid DNAs eontain a major virion sense ORF and are transeribed unidirectionally. However,two mRNAs (eneoding M-Rep and U5 protein) are transcribed lrom the BBTV DNA-R, whereas allthe other babu- and nanovirus DNAs (incl. the other babu- and nanovirus DNA-R) seem to eneodea single protein only. Eaeh eoding region is preeeded by a promoter sequence with a TATA box and10Uowed by a polyadenylation signal (Figures 2 and 3). For the nanovirus D A-R, however, the posi­tion 01 the polydenylation signal between the TATA box and the ORF leads to transeription 01 the rep­lication origin and synthesis of a terminally redundant mRNA that is eapable 01 lolding into extendedseeondary struetures. This may be a way to regulate the expression 01 the eneoded master replieationinitiator (M-Rep) protein.

5ince the nanovirid DNAs and some 01 the biochemiea! events determined lor nanovirid replicationresemb!e those 01 the geminiviruses, their replieation is also thought to oceur in the nucleus throughtranscriptionally and replieationally aetive dsDNA intermediates by a rolling circle type 01 repliea­tion meehanism. Upon deeapsidation 01 viral ssDNA, one of the first events is the synthesis of viraldsDNA with the aid 01 host DNA polymerase. As the virus 0 As have the ability to self-primeduring dsDNA synthesis, it is like!y that pre-existing primers are used lor dsD A replieative lorm(RF) synthesis, as has been shown for BBTV. From these dsDNA lorms, host RNA polymerase thentranseribes mRNAs eneoding the M-Rep and other viral proteins. Viral DNA replieation is initiatedby the M-Rep protein. There is experimental evidenee for laba bean neerotie yellows virus (FBNYV)and BBTV that M-Rep has DNA eleavage and nucleotidyl transler aetivity iJl vitra and initiates thereplieation of all genomic DNAs. These biochemiea! reactions involve a eonserved nonanueleotidesequenee flanked by inverted repeat sequenees that potentially lorm a stem-Ioop strueture and areapart 01 the viral origin of replieation (ori). This sequenee arrangement including the loop-Iormingsequenee eontaining the nonanueleotide TATIATIAC or TAGTATIAC is perleetly eonserved inbabuviruses and nanoviruses, respeetively. The non-eoding regions (NCRs) 01 all genomie 0 As01 a given nanovirid share this highly eonserved stem-Ioop region (CR-5L) that also eneompassesshort repeated sequenees (iterons) that are presumed to be binding sites lor the M-Rep protein, theonly viral protein essential lor nanovirus replieation. All other replieation proteins including DNA

397

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Subterranean clover stunt virus

NANOVIRUS

discrimination within a genus. Although species-speeifie monocJonal antibodies (where available)can be used for speeies diserirnination, preference should nowadays be given to the molecular crit­eria specified above.

Table 2: Features distinguishing viruses of the genera NallovirIls and BabuvirIls

Nn1'loviridae

Distinguishing featuresExperimental and circumstantial evidenee suggests that the nanovirus genome eonsists of eight dif­ferent ssONA eomponents, referred to as DNA-R, -S, -M, -C, -N, -UI, -U2 and -U4 (Figure 2). TI,US,the latter three DNAs are characteristie for viruses of the genus NanDvi,."s. The other major differ­ences between babu- and nanoviruses are that the latter natllrally infect legurnes (dicots), are vec­tored by several aphid species colonizing legumes, and share low levels of aa seguenee identitiesranging from 18 to 56% in individual genes with babuviruses. Moreover, the nanovirus DNA com­ponents ranging in size from 923 to 1020nt are slightly smaller (by ca. lOOnt) than those of babuvi­ruses (1013-1111 nt) and, in contrast to babuviruses, the nanovirus DNA-R transeripts are terminallyredundant.

..z.. CR-SL _ eR·1I ...... ORF • TATA box ~ polyadenylation signal

399

GENUS

Features Genus Nnnovirus Genus Babuvirus

Major hosts Oieots (legumes) Monocots

Major aphid vectors Aphis craccivorn and a few other Pelltn/onia and Micromyzfls spp.legume-colonizing aphid species

No. of genomic DNAs 8 6

Presence of specific DNAs DNA-Ul, -U2, -U4 DNA-U3Size of genomic DNAs 923-1020nt 1013-1111 ntOverall nucleotide sequence relationship in >50% (between species) >50% (between species)DNA-R, -N, -5, -C and -M <45% (between babu- and nanoviruses)

Type species

Figure 2: Diagram iIlustrating the genornic organization of viruses of the genus Natlovirus and depicting the structure of theeight identifiea viral DNA components (see afso Table 1). Each DNA cirde (1000 :!: 20nt) contains its cfesignated name andthe name of the encoded protein. Arrows refer to the location and approximate size of the ORFs and the direction of tran­scription. Note that DNA-U2 and -U4 have not been identified frorn SCSv. The position of the common stern-Ioop region(CR-5L) and the second common region (CR·lT) are indieated.

Differenees in natural host rangeDifferenees in the number and types of veetor aphid speeiesDifferent reaetions to antibodies to individual speciesDifferenees in CP aa sequences of >15%, and/orOverall nt sequenee identity of <75% is generally indieative of a distinet speeies.

Sinee several nanovirids are now known to have overlapping host ranges and to be transmit­ted by a similar range of aphid speeies, biologieal eriteria appear no longer useful for speeies

•

polymerases are provided by the host eell. Viral D A replieation is enhaneed by the action of Clink,a nanovirid-eneoded eell eyde modulator protein.

••

Criteria to be used as guidelines for species demarcation are:

••

HOST RANGEViruses of the individual speeies have narrow host ranges. anoviruses naturally infeet only alimited range of leguminous speeies (Fabaeeae), whereas babuviruses have been reported onlyfrom few monoeots, such as the Musaeeae and Zillgiberaeeae. All viruses are assoeiated with stunt­ing of infeeted plants, and infected hosts mayaiso show leaf roll, ehlorosis and premature death.

anovirids are restrieted to the phloem tissue of their host plants and are not transmitted meehani­eally or through seeds. Until recently, plants eould only be experimentally infeeted by graft orveetor transmission. However, infeetivity of purified FBNYV virions by biolistie bombardmenthas now been demonstrated and aphid-transmissible FBNYV and faba bean neerotie stunt virus(FBNSV) virions have been reeonstituted using eight doned DNAs.

TRANSMISSIONUnder natural conditions, all viruses are transmitted by certain aphid species in a persistent man­ner and do not replieate in their veetors. Together with resulls from eomplementation experiments,there is evidenee that veetor transmission of FBNYV (and probably also other nanovirids) requirea virus-eneoded helper faetor that is either dysfunetional or absent in purified virion preparations.

GEOGRAPHICAl DISTRIBUTIONWhile BBTV is widely distributed in banana growing countries in the Asia-Paeifie region andAfriea, ABTV has been reported only from Sarawak (Malaysia) and the Philippines, and CBDVonly from India. SCSV oeeurs in Australia, milk veteh dwarf virus (MOV) in China and Japan, peaneerotie yellow dwarf virus (PNYDV) in Europe and FB SV in Ethiopia and Moroeco. In eontrast,the reported geographie distribution of FBNYV is mueh wider, oecurring in several countries ofWest Asia and orth and East Afriea as weil as in a European eountry (Spain). 0 nanovirus hasbeen reeorded from the New World.

In addition to the genomie DNAs, a number of additional D As encoding Rep proteins have beenfound assoeiated with some, but not all nanovirid infeetions. These additional DNAs, referred toas "alphasatellites" (see ehapter on "Satellites"), are genetieally very diverse and phylogenetieallydistinet from the DNA-R of nano- and babuviruses. Tentative evidenee suggests that these DNAsinterfere with the establishment and expression of nanovirid disease symptoms.

Part 11 - TJre Single Siranded ONA VirIlses

Biological properties

Genus and species demarcation criteria in the familyFeatures demareating the two genera in the family, i.e., eriteria to be used for distinguishing babuvi­ruses from nanoviruses, are shown in Table 2.

Antigenic propertiesVirions are strong immunogens. Most viruses belonging to the same genus are serologieally relatedto, but distinet from, one another. No serologiea] relationship between babu- and nanoviruses hasbeen observed.

Part II - Tlie Sillgle Slmllded DNA Vil"llses Nanovirirlae

Species names are in italic script; names of isolates are in roman script. Sequence accession numbers 1I and assignedabbreviations () are also Iisted.

Nanoviruses have largely overlapping but relatively narrow host ranges. They infeet over 50 leg­ume species and only a few non-Iegume species under experimental and natural conditions. Theyare transmitted by several aphid speeies. Apliis cmceivom appears to be the major natural veetor ofthese viruses as it is the most abundant aphid speeies on legume erops in the afflieted areas andwas among the most effieient veetors under experimental eonditions. Other aphid veetors areAcyrtilOsipllOlI pisl/l11 and Apliis labae but for MDV also A. gossypii and Megol/m vieiae.

Antisera to FBNYV and SCSV eross-reaet weakly with SCSV and FBNYV respeetively in Westernblots and immunoeleetron mieroseopy, but not at all in DAS-ELISA, suggesting that the serologi­eal relationship between these two viruses is distant (CP aa sequenee identity ca. 57%). However,MDV and FBNSV reaet strongly not only with FBNYV antisera but also with the majority of mon­odonal antibodies to FBNYY. Therefore, speeies-speeifie MAbs are required for the differentiationand speeifie deteetion of these three dosely related speeies, whieh share CP aa sequenee identities of83--85%.

List of species in the genus NanovirusFaba beatl lIeerafie ycllows virlls

Faba bean necrotic yellows virus-IEgyptlFaba bean necrotic yellows virus-[Morocco)

Milk vetcll dwar! virusMilk vetch dwarf virus-Uapan)

Sl/bterralleall daver stUllt virusSubterranean clover stunt virus-[Australia)

IAj132179 to -84, AJ132186, AJ749902]IGQ274023 to -30)

[AB000923 to -7; ABOO9046, AB027511,AB044387, AB255373]

IU16730, U16732-4, U16736, AJ290434}

(FBNYV-IEGj)(FB YV-IMA])

(MDV-IJPj)

(SCSV-IAUj)

BBTV and ABTV have a genome eonsisting of six different ssDNA eomponents, referred to asDNA-R, -S, -C, -M, - ,and -U3 (Figure 3). Sinee they have been identified from all babuvirus iso­lates studied in greater detail, they are eonsidered integral eomponents of the babuvirus genome.Although there are several BBTV isolates from whieh a DNA-U3 has not been identified, mostbabuviruses seem to possess a speeifie DNA eomponent (DNA-U3) of unknown funetion. Only forDNA-U3 of BBTV-[AU) (L41576) has an RNA transeript been reported.

Unlike the relative eonservation among the genes within nanovirus speeies, there is eonsiderablevariation in eertain genes among individual isolates of a babuvirus speeies. Striking genetie differ­ences ranging from 7 to 20% have been observed for the individual gene products of two ABTVisolates, one from the Philippines and the other from Sarawak (Malaysia). Similarly, two groupsof BBTV isolates, designated the Asian and South Pacific groups, are distinguished based onDNA-R, -N and -S sequences. The nt sequenees of the major gene of DNA-R, -N and -S differ by 7.5,8.6 and 6.3% whieh translate to mean differenees of 5.6, 6.7 and 1.4%, respeetively, in aa sequeneesbetween the two geographie groups. Partieularly striking are the differenees between the twogroups of BBTV isolates in the CR-M of 0 A-R (32%), -N (27%) and -S (39%), whereas the intra­group CR-M variation does not exeeed 6%. Whereas the DNA-R, - and -S genes appear to be weilconserved among BBTV isolates, striking differenees (up to 19%) between BBTV isolates in less eon­served gene produets (e.g., movement protein) have been observed (Figure 4). If these genetie dif­ferenees ean be substantiated by eompletely sequeneing a number of Asian isolates, this might formthe basis for a future subdivision of BBTV into two separate speeies.

BBTV is serologieally unrelated to members of the genus NmlOvirus. However, BBTV antibodieshave been used for the deteetion of ABTV and CBDV, the two other babuviruses. Of 10 monoclonalantibodies raised to BBTV, only two reaeted with ABTV. This is eonsistent with a CP amino acidsequenee differenee of about 20% between ABTV and BBTV.

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IGU553134']

[GQ150778 to -85][GQ274031 to -81

List of other related viruses which may be members of the genus Nanovims but have notbeen approved as species

Faba beatl Ilecrotic stUIl! virusFaba bean necrotic stunt virus-[Ethiopia]Faba bean necrotic stunt virus-[Moroccol

Pea llecrotic ye/low dwarfvirusPea necrotic yellow dwarf virus-[Germany]

.. Although only a DNA-R sequence has been described for PNYDV-[DEj (Grigoras et al., Plall! Dis. 94,643,2010), the sevenother genome segments have been sequenced and aphid transmissible virus has been reconstituted using cloned DNAs.

GENUS BABUVIRUS

D~:;N )oDNA-U3'

U3 J

Type species Banana bunchy top vinls

Distinguishing featuresBabuviruses naturally infeet monocots (Musa and Amomum spp.) and are veetored by the bananaaphid Pelltalollia Iligrol/ervosa (CBDV also by Micromyzus kalimpollgellsis Basu). BBTV and ABTVinfeet bananas (Musa spp.) and c10sely related speeies within the MI/saceae, such as M. textilis eeand Ellse!e velltricosl/m Cheesem. There are no eonfirmed non-Musa hosts of BBTV and ABTV.Symptoms of BBTV indude plant stunting, foliar yellowing and most eharaeteristie dark greenstreaks on the pseudostem, petioles and leaves. There is not much information on CBDV, whichhas reeently been found associated with a serious disease ("Foorkey") of large eardamom (Amomumsl/bl/latum Roxb.) in India.

..t. CR-$L _ CR-M ..... ORF • TATA box ~ polyadenylation signal

F.ig~re 3:..Diag~am iIIustrating the genomic organization of viruses?f the genus Babuvirtls a~d d.epicting the structure of theSIX ldentlfled viral DNA components (see also Table 1). Each DNA clrele (1060 ± 50nt) contams Its designated name and thename of the encoded protein. The position of the common stem-Ioop region (CR-SL) and the major common region (CR-M)are indicated. Arrows refer to the loeation and approximate size of the ORFs and the direction of transcription. Note that (i)no ORF has been identified from D A-U3 of the two ABTV isolates and several Asian isolates of BBTV and (ii) DNA-R ofBBTV has a small internaI ORF which potentially encodes a SkDa protein (US) and has been shown to be transcribed fromDNA-R of BBTV-[AUI.

400 401

Part [[ - Tile Sillgle Stranded DNA Viruses Nanoviridae

Species namcs are in italic script; names of isolates are in roman script. Sequence accession numbers [J and assignedabbreviations () are also listed."Although the DNA-R sequence available from GenBank is defective, an apparently complete DNA-R sequence has beendetermined.

List of other related viruses which may be members of the genus BabllvirllS but have notbeen approved as species

None reported.

List of unassigned species in the family Nanoviridae

100r---;:=:..-_ SCSV-{AULAJ290434

r--- PNYDV-[DELGU553134FBNSV-[MALGQ274033

FBNSV-[ETLGQ150778 Nanov;rusFBNYV-[MALGQ274025FBNYV-[EGLAJ132180

DV- JP AB027511

•• •BBTV·fTWLD0826390

CBOV;INLAY485960 BabuvlrusABTV-[MYLEF546813

DNA.R '- """A~B!.!TV~.JJ:P:!:!HbE5!F:.i!54:!!..!!!Oi!.(7 ....

~ SCSV-{AULU16733

~FBNSV'[MALGQ27403'FBNSV-[ETLGQ150782 Nanov;rus

FBNYV-[MALGQ274030

- 100 FBNYV-[EGLAJ132186. MDV-[JPl_ABOOO925

oBTV·[AUQ:41577BBTV{IWLOQ826396

Babuv;rus100~ ABTV-[MYLEF546808

DNA-N ABTV-le:Hl EF546802

(ABTV-[MY])(ABTV-[PH])

(BBTV-[AU])(BBTV-[TW])

(CdBDV-[IN])[AY485960']

[EF546808 to -13][EF546802 to -7]

[556276, L41574 to -781[DQ826390 to -1; DQ826393 to -6]

List of species in the genus BabllvirllsAbnen bunchy top vims

Abaca bunchy top virus-[Malaysia]Abaca bunchy top virus-[Philippines]

Ba/lana bunchy top virusBanana bunchy top virus-[Australia]Banana bunchy top virus-[Taiwanl

Cnntall10m bllshy dwar! virusCardamom bushy dwarf virus-[lndia]

Species names are in italic script; names of isolates are in roman script. Sequence accession numbers [ J and assignedabbreviCltions ( ) are also listed.*Since this appears to be an alphasatellite sequence, it should no Ionger be assigned to the family Nalloviridae.

Phylogenetic relationships within the familyAnalysis of the five proteins identified from the majority of the assigned nanovirid species (Figure 4)suggests that the most conserved nanovirid proteins are the M-Rep protein (54-97% identity) andthe NSP (41-91%), followed by the CP (20-84%), the MP (14-76%) and the Clink protein (18-72%).Babuviruses share significant levels of aa sequence sunilarity with nanoviruses only in the M-Rep(54-56%) and NSP (41-45%), whereas the aa sequence similarities between the two genera are negli­gible in the CP (20-27%), the MP (20-23%) and the Clink protein (18-23%).

Similarity with other taxaAll Rep proteins of the assigned species have most of the aa domains characteristic of Rep pro­teins of geminiviruses and other ssDNA viruses. The nanovirus Rep proteins differ from those ofmembers of the family Geminiviridae in being smaller (about 33 kDa), having a slightly differentdNTP-binding motif (GPQ/NGGEGKT), lacking the retinoblastoma-like protein (Rb)-binding motif(LxCxE) and sharing aa sequence identities of only 17 to 22% with them. Moreover, the assignedspecies are clearly distinct from geminiviruses in particle morphology, genome size, number andsize of DNA components, mode of transcription, and in vector species. Although circo- and nano­virids possess closely related Rep proteins and morphologically sirnilar virions, circovirids infectvertebrates and have a much smaller genome (1.8-2.3kb) that is not only monopartite but also bidi­rectionally transcribed. All these ssDNA viruses have a conserved nonanucleotide motif at the apexof the stem-Ioop sequence which is consistent with the operation of a rolling circle model for DNAreplication.

Nanov;rus

-----------r---======---- SCSV-[AULU16734----­

92'------ FBNSV-[MALGQ274036L..-- FBNSV-[ETLGQ150779

99'---- FBNYV-[MALGQ274028

-~,;:~E=========:~~~~~~~~F~BiNYV~'[~E~G1L~AJ!'~32:':83::::::::::~MDV-[JPLAB009046

100 4b,.

BB~~fTWLDa826393.....-- ABTV.(MYLEF546810 Babuvlrus

DNA-S 97 ABTV.!!'Hl EF546B04

~ SCSV-(AULU16730

99 100 FBNSV-{MALGQ27403585 FBNSV-[ETLGQ150781

MDV-IJPLABOOO927 Nanov;rus

- ~ FBNYV-[MALGQ27402795 FBNYV-[EGLAJ132182

100 BBTV-(AULL.41575BBTV·(TWLOQ826394

100 ABTV-{MYLEF546811 Babuvirus

DNA·M 100 ABTV-[PHLEFS46805

I ~BNSV-[MALGa274031

FBNSV-[ETLGQ150780~ '00 FBNYV-[MALGQ274023

99 FBNYV-[EGLAJ132179 Nanov;rusMDV·[JPLABOOO923

- SCSV.[AULU16732100 BBTV.[AlJi·l41578

BBTV-[TWLDQ826395

""I ABTV·IMYLEF546812 Babuv;rus

DNA-C 100 ABTV·IPH! EF546806

(CFDV-[VU])[M29963'JCOCOl1l1t foliar decay virus

Coconut foliar decay virus-[Vanuatu]

Derivation of namesBab,,; from banana bunchy top virus.Nano: from the Greek nanos, meaning "dwarf", referring to the observations that these plant viruseshave the smallest known virions and genome segment sizes, and dwarf their hosts.

Figure 4: Nei!?hbor-joining dendrograms illustrating nucleotide sequence relationships in the five DNAs (DNA-R, -N, -S, -Cand ·M) identIfied from aß assignea and (still) putative members oI the genera Nanovirus and Babllvirus (family Nanoviridae):abaca bu~chy top virus (ABTV), banana bunchy top virus (BBrV), cardamom bushy dwarf virus (CBDV), faha bean necroticy~llows VIrUS (FBNYV), faha bean necrotic stunt VlfUS (FBNSV), milk vetch dwarf virus (MDV), pea necrotic yellow dwarf~Jrus (PNYDV), and subterrane~ clover stu~t virus (SCSV). Since seque.nc.e in~orn:ation is available for genetically distinctlsolates of some nano- and babuvlruses and thlS rnay have future taxonomIC IrnpltcatIons, the sequences of ABTV isolates fromMalaysia (MY) and the Philippines (PH), BBTV isolates from Australia (AU) and Taiwan (TW), FBNYV isolates from Egypt(EG) and Morocco (MA), ana FBNSV lsolates from Ethiopia (ET) and Morocco (MA) were included in the comparison. VertIcalbranch lengths a~e arbitrary and horizontal distances are proportional to the number of base substitutions per site (see scalebar). Sequence ahgrunents and de!ldrograms were produced using DNAMAN (version 6, Lynnon Biosoft, Quebec, Canada)which uses a CLUSTAL-type algonthm. The dendrograms were bootstrapped 1000 times (scores are shown at nodes).

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Part Il- Tlie Single Sirnnded DNA Virllses

Further readingBums, T.M., Harding, R.M. and Dale, ].L. (1995). The genome organization of banana bunchy top virus: analysis of six

ssDNA components. f. Gen. Virol., 76, 1471-1482.Chu, P.W.G. and Vetten, H.J. (2003). Subterranean dover stunt virus. MB Descriptiol/s 0/ Plnllt Vimses, 396.Grigoras, 1., Gronenborn, B. and Vetten, H.J. (2010). First report of a nanovirus disease of pea in Germany. PInnt Dis., 94, 643.Grigoras, 1., Timchenko, T. , Grande-Perez, A., Katul, L., Vetten, H.J. and Gronenborn, B. (2010). High variability and rapid

evolution of a nanovirus. f. Virol., 84, 9105-9117.Grigoras, 1., Timchenko, T. and Gronenborn, B. (2008). Transcripts encoding the nanovirus master replication initiator protein

are terminally redundant. f. Gen. Virol., 89, 583-593.Grigoras, L, 1imchenko, 1., Katul, L. , Grande-Perez, A., Vetten, H.}., and Gronenborn, B. (2009). Reconstitution of authentie

nanovirus from multiple cJoned 0 As. /. Virol., 83, 10778-10787.HUt J.M., Fu, H,C, Un, CH., Su, H.J. and Yeh, H.H. (2006). Reassortment and concerted evolution in banana bunchy top

virus genomes. /. Viral., 81, 1746-1761.Karan, M., Harding, R.M./and Dale, J.L. (1994). Evidence for two groups of banana bunchy top virus isolates.}. Gell. Viral., 75,

3541-3546.Sharman, M., Thomas, J.E., Skabo, S. and Holton, T.A. (2008). Abaca bunchy top virus, a new member of the genus Hobl/virus

(family NmlOviridne). Arcll. Viral., 153, 135-147.Velten, H./. (2008). anoviruses (3rd edn.). In B.W.) Mahy and M.H.Y. Van Regenmortel (Eds.), ElloJclopedin of Virology (val. 3,

pp. 385-391). Oxford: Elsevier.

Contributed byVetten, H.]., Date, J.L., Grigoras, 1., Gronenborn, B., Harding, R, R(lndles, j.W., Sano, Y, Thomas, J.E., Timchenko, 1. and

Yeh, H.H.

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