Geminiviridae
From Wikipedia, the free encyclopedia
| Geminiviridae | ||||
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Mastrevirus |
Geminiviruses are plant viruses which have ambisense single-stranded circular DNA genomes and are members of class II of the Baltimore classification of viruses. The genome can either be segmented (2500-3000 nucleotides) or non-segmented (4800-5600 nucleotides). They have an elongated, geminate capsid with incomplete T=1 icosahedra joined at the missing vertex. The capsids range from 18-20 nm in diameter with a length of 30nm. Viruses with bipartite genomes (begomoviruses only) have these components separated into two different particles, therefore more than one virus particle is required to infect a cell.
Transmission of these viruses can be via leafhoppers or via one species of whitefly or via treehoppers.
Purified Maize streak virus (MSV) particles stained with uranyl acetate. Size bar indicates 50 nm. Picture courtesy of Kassie Kasdorf.
The Geminiviridae include the following genera:
- Genus Mastrevirus; type species: Maize streak virus
- Genus Curtovirus; type species: Beet curly top virus
- Genus Begomovirus; type species: Bean golden mosaic virus
- Genus Topocuvirus; type species: Tomato pseudo-curly top virus
These viruses are responsible for a significant amount of crop damage worldwide. Epidemics of geminiviruses have arisen due to the recombination of geminiviruses coinfecting a plant, enabling novel, virulent strains to be developed. Other contributing factors include the transportation of plant material and the expansion of vectors that can spread the virus from one plant to another.[1]
[edit] Replication
Geminiviruses encode only a few viral proteins, thus they are dependent on their host cell in order to replicate and require host factors such as DNA polymerase in order to amplify their genomes. Geminiviruses replicate via a rolling circle mechanism like bacteriophages such as M13. Replication occurs within the nucleus of an infected plant cell. Firstly the single-stranded circular DNA is converted to a double-stranded circular intermediate. This step involves the use of cellular enzymes to produce a complementary negative-sense strand using the viral plus-sense DNA strand as a template. The next step is the rolling circle phase whereby the viral strand is cleaved at a specific site situated within the origin of replication by a viral protein such as Rep protein in order to initiate replication.[2] Consequently new single-stranded DNA forms of the virus (plus-sense) are formed, which are then packaged into germinate particles. These particles can then leave the nucleus and be transmitted to surrounding cells in association with movement proteins via the plasmodesmata.[3]
These viruses tend to infect differentiated plant cells, but these cells lack host enzymes making it difficult for the virus to replicate. To overcome this geminiviruses can induce plant cells to reenter the cell cycle from a quiescent state so that viral replication can occur.[4]
[edit] References
- Description of Plant Viruses
- MicrobiologyBytes: Plant Viruses
- International Committee on Taxonomy of Viruses
- ^ Gray and Banerjee (1999). "Mechanisms of arthropod transmission of plant and animal viruses". Microbiol Mol Biol Rev. 63 (1): 128-148. PubMed.
- ^ Chasan R (1995). "Geminiviruses: A Twin Approach to Replication". Plant Cell 7 (6): 659-661.
- ^ Gutierrez C (2000). "DNA replication and cell cycle in plants: learning from geminiviruses". EMBO 19 (5): 792-799. PubMed.
- ^ Hanley Bowdoin lab
