Potyviridae

Genus: Ipomovirus


Genus: Ipomovirus

Distinguishing features

Ipomoviruses are distinguished from other genera by their mode of transmission being whiteflies, and by phylogenetic analyses.

Virion

Morphology

Virions are flexuous filaments 800–950 nm long.

Physicochemical and physical properties

Vision Sedimentation coefficient S20,w is 155S for sweet potato mild mottle virus (SPMMV).

Nucleic acid

Virions contain a single molecule of linear, positive sense ssRNA, about 9.7 kb in size; virions contain 5% RNA by weight.

Proteins

The viral CP is a single polypeptide of 302–378 aa (35–41 kDa). 

Genome organization and replication

Ipomoviruses exhibit unusual structural variability. The structure and organization of the SPMMV genome is similar to that of members of Potyvirus (Figure 2.Potyviridae), but some motifs of HC-Pro and CP characteristic of Potyvirus are incomplete or missing, which may account for its vector relations. The unusually large P1 protein (83 kDa) of SPMMV contains no obvious AlkB domain and hence differs from that found in members of the genus Brambyvirus. Cucumber vein yellowing and squash vein yellowing viruses (CVYV and SqVYV) differ from SPMMV by encoding two P1-like serine proteases (P1a and P1b) but no HC-Pro. P1b functions as a suppressor of RNA silencing (Li et al., 2008). Cassava brown streak virus (CBSV) differs from SPMMV by having no HC-Pro and, also, from CVYV and SqVYV by having only P1b which suppresses silencing (Figure 1.Ipomovirus). Additionally, CBSV contains a Maf/HAM1-like sequence recombined into the NIb/CP junction, which can accommodate heterologous genes in engineered infectious potyvirus clones. Homology of HAM1h with cellular Maf/HAM1 NTP pyrophosphatases suggests that HAMh1 might intercept non-canonical NTPs to reduce mutation rates of viral RNA.

Figure 1.Ipomovirus. Genomic maps of the ipomoviruses sweet potato mild mottle virus (SPMMV), squash vein yellowing virus (SqVYV) and cassava brown streak virus (CBSV). The ssRNA genome is represented by a line and an open box representing the ORF translated into a polyprotein. Conventions are as for the potyvirus genome organization map (Figure 2.Potyviridae). Activities of most mature proteins are postulated by analogy with genus Potyvirus. CVYV and SqVYV contain two P1-like serine proteases (P1a and P1b), of which P1b functions as a suppressor of RNA silencing. CBSV also contain P1b which suppresses silencing and, additionally, carries a Maf/HAM1-like sequence recombined into the NIb/CP junction. HAMh1 might intercept non-canonical NTPs to reduce mutation rates of viral RNA.

Antigenicity

Moderately immunogenic. No serological relationships with other members of the family Potyviridae have been found.

Biology

Host range

The natural host range of SPMMV is wide, with more than nine families susceptible, whereas the host range of CBSV, CVYV and SqVYV is less known apart from the hosts which they have been found to infect in the field (Winter et al., 2010).

Transmission

CBSV, CVYV and SqVYV are transmitted by the whitefly Bemisia tabaci in a non-persistent manner. B. tabaci may also be the vector of SPMMV, but this is not fully confirmed. All ipomoviruses are transmissible experimentally by mechanical inoculation and by grafting.

Derivation of names

Ipomo: from Ipomea and mosaic, the symptoms induced on the host of the type species.

Member Species

SpeciesVirus name(s)Exemplar isolateExemplar accession numberExemplar RefSeq numberAvailable sequenceOther isolatesOther isolate accession numbersVirus Abbreviation(s)
Cassava brown streak viruscassava brown streak virusKOR6GU563327NC_012698Complete genomeCBSV-KOR6
Cucumber vein yellowing viruscucumber vein yellowing virusSpain ALM32AY578085NC_006941Complete genomeCVYV-ALM32
Squash vein yellowing virussquash vein yellowing virusFlorida EU259611NC_010521Complete genomeSqVYV-FL
Sweet potato mild mottle virussweet potato mild mottle virusEast AfricaZ73124NC_003797Coding complete genomeSPMMV-EA
Tomato mild mottle virustomato mild mottle virusEthiopia HE600072Complete genomeTMMoV-Ethiopia
Tomato mild mottle viruseggplant mild leaf mottle virusIsraelHQ840786EMLMV-Israel
Ugandan cassava brown streak virusUgandan cassava brown streak virusUG Uganda:Namulonge.2004FJ185044NC_014791Complete genomeUCBSV-UG

Virus names, the choice of exemplar isolates, and virus abbreviations, are not official ICTV designations.
Download GenBank/EMBL query for sequences listed in the table here.

Related, Unclassified Viruses

Virus name

Accession number

Virus abbreviation

Coccinia mottle virus

KU935732

 CocMoV

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

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