Geminiviridae

Maize streak virus, in the family geminiviridae. Courtesy of Dr. John Antoniw. From Rothamsted's Electron Micrographs of Plant Viruses

Baltimore Classification

Higher order taxa

Virus; ssDNA viruses; Geminiviridae

Genera

Mastrevirus, Begomovirus, Topocurvirus, Curtovirus

Description and Significance

Geminiviruses are DNA plant viruses transmitted by insects, namely leafhoppers and whiteflies. The genera are distinguished by the type of plant they infect, the number of DNA segments, and the type of vector. Geminiviruses can wipe out entire crops of many different plants (such as tomatos, beans, corn, cassava, and cotton), making them a serious threat to farming industry worldwide. (sources: Microbiology @ Leicester, Rybicki)

Genome Structure

Geminiviruses have circular single-stranded DNA. The genome is either in two segments or not segmented at all. The non-segmented genome is 2500-3000 nucleotides long, and the segmented genome is 4800-5600 nucleotides long. The genome encodes for both structural and non-structural proteins. In geminiviruses with the segmented genome, both segments must be transmitted to the host for a full systemic infection to occur. (source: ICTVdB, Descriptions of Plant Viruses)

Virion Structure of a Geminivirus

Twinned isohedra. From Descriptions of Plant Viruses

Geminiviruses are non-enveloped, icosahedral virions that consist of a capsid. The capsid is geminate, or twinned, and consists of 22 capsomers. The capsid is 30nm long and has a diameter of 18-20nm. (source: ICTVdB)

Reproductive Cycle of a Geminivirus in a Host Cell

Geminivirus is transmitted to host plants by way of insects. Geminiviruses only encode for a few proteins, so it only supplies the DNA for viral replication and uses the host's DNA replication proteins to amplify its genome. The viral single-strand DNA is converted to double-strand DNA, which is then used to amplify viral double-strand DNA and replicate single-strand DNA genomes. Geminiviruses also control the host plant's cell cycle, allowing cells in which the virus has used up its DNA replicating capabilities to regain the ability to support high levels of (viral) DNA replication. (sources: The Hanley-Bowdoin Lab, Gutierrez)

Interestingly, geminiviruses are one of the few plant virus families which uses a DNA genome. According to Rojas et al., most plant viruses use an RNA genome, which suggests that plants have controlled the evolution of DNA viruses. Geminiviruses evolved the ability to control the cell cycle (which was mentioned previously), several strategies for cell-to-cell and long-distance movement, and ways to get around the host's antiviral systems as a response to the impediments to DNA viruses plants have created. Because of these abilities that geminiviruses have, they have become one of the most deadly plant pathogens in the world, causing devastating crop losses worldwide.

Viral Ecology & Pathology

Geminiviruses infect numerous different plants, and new strains emerge often, as the virus swaps genetic material with other strains. The spread of infection is limited to the ecosystems where the carrier insects live, which tend to be temperate climates that are also good for growing crops. (source: Moffat)

References. Updated June 5, 2006

Descriptions of Plant Viruses - Notes on Family: Geminiviridae

Gutierrez C. "Geminivirus DNA replication." Cell Mol Life Sci. 1999 Oct 15;56(3-4):313-29.

The Hanley-Bowdoin Lab - Geminivirus - Host Interactions

ICTVdB - The Universal Virus Database, version 3. http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/

Microbiology @ Leicester: Virology: Plant Viruses

Moffat, Anne Simon. "Geminiviruses Emerge as Serious Crop Threat." Science 286 (1999): 1835.

Rojas et al. "Exploiting chinks in the plant's armor: evolution and emergence of geminiviruses." Annu Rev Phytopathol. 2005;43:361-94.

Rybicki, Ed. The Maize Streak Virus Home Page - Geminiviridae