Geminiviridae
| Geminiviridae | |
|---|---|
 |
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| Purified Maize streak virus (MSV) particles stained with uranyl acetate. Size bar indicates 50 nm. | |
| Virus classification | |
| Group: | Group II (ssDNA) |
| Order: | Unassigned |
| Family: | Geminiviridae |
| Genera | |
Geminiviridae is a family of plant viruses. There are currently 325 species in this family, divided among 7 genera. Diseases associated with this family include: bright yellow mosaic, yellow mosaic, yellow mottle, leaf curling, stunting, streaks, reduced yields. They have single-stranded circular DNA genomes encoding genes that diverge in both directions from a virion strand origin of replication (i.e. geminivirus genomes are ambisense). According to the Baltimore classification they are considered class II viruses. It is the largest known family of single stranded DNA viruses.
Mastrevirus transmission is via various leafhopper species (e.g. maize streak virus and other African streak viruses are transmitted by Cicadulina mbila), curtoviruses and the only known topocuvirus species, Tomato pseudo-curly top virus, are transmitted by treehopper species (e.g.Tomato pseudo-curly top virus is transmitted by the treehopper Micrutalis malleifera), and begomoviruses are transmitted by the whitefly species, Bemisia tabaci.
These viruses are responsible for a significant amount of crop damage worldwide. Epidemics of geminivirus diseases have arisen due to a number of factors, including the recombination of different geminiviruses coinfecting a plant, which enables novel, possibly virulent viruses to be developed. Other contributing factors include the transport of infected plant material to new locations, expansion of agriculture into new growing areas, and the expansion and migration of vectors that can spread the virus from one plant to another.
The genome can either be a single component between 2500–3100 nucleotides, or, in the case of some begomoviruses, two similar-sized components each between 2600 and 2800 nucleotides. They have elongated, geminate capsids with two incomplete T=1 icosahedra joined at the missing vertex. The capsids range in size from 18–20 nm in diameter with a length of about 30 nm. Begomoviruses with two component (i.e. bipartite) genomes have these components separated into two different particles both of which must usually be transmitted together to initiate a new infection within a suitable host cell.
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