Family: Geminiviridae
Genus: Topocuvirus
Distinguishing features
Tomato pseudo-curly top virus (TPCTV) is the only member of the genus. The virus has a monopartite genome that encodes six genes with an organization similar to that of the genomes of monopartite begomoviruses. TPCTV is the only geminivirus known to be transmitted by a treehopper (Micrutalis malleifera). The virus infects only dicots, and has been identified only in the southeastern United States (Briddon et al., 1996).
Virion
See discussion under family description.
Genome organization and replication
The genome of TPCTV consists of a single component of circular ssDNA of 2.8 kb. The genome, encoding six proteins, resembles that of monopartite members of the genus Begomovirus (Figure 1. Topocuvirus). Nucleotide sequence comparisons suggest that TPCTV and begomoviruses diverged after a recombination event altered insect vector specificity (Briddon et al., 1996). The coat protein (gene V1) is more closely related to those of the leafhopper-transmitted curtoviruses than to those of the whitefly-transmitted begomoviruses. The V2 protein is distantly related to the curtovirus V2 protein.
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Figure 1. Topocuvirus. Genomic organization of topocuviruses. ORFs are denoted as either being encoded on the virion-sense (V) or complementary-sense (C) strand. The position of the stem-loop containing the conserved 5′-TAATATTAC-3′ sequence located in the intergenic region (IR) is shown. |
Biology
Host range
The host range of TPCTV is restricted to dicotyledonous plants, and includes weed species such as nightshade (Solanum nigrum), Datura stramonium and common chickweed (Stellaria media), crops such as tomato and common bean, and the experimental host Nicotiana benthamiana. TPCTV induces symptoms resembling those associated with BCTV infection in many hosts (Briddon et al., 1996).
Transmission
TPCTV is transmitted in nature by the treehopper Micrutalis malleifera Fowler (order Hemiptera, family Membracidae), and has been transmitted experimentally to plants by Agrobacterium-mediated transfer (agroinoculation) from a tandemly repeated cloned genomic DNA (Briddon et al., 1996).
Antigenicity
The TPCTV virion is antigenically closely related to that of beet curly top virus (BTCV) in the genus Curtovirus.
Species demarcation criteria
Not applicable.