Geminiviridae

Abstract The Geminiviridae comprise a group of plant viruses with small, circular, single‐stranded deoxyribonucleic acid (ssDNA) genomes encapsidated in particles that have a twinned quasi‐icosahedral (geminate) shape, from which the family derives its name. They are among the smallest of viruses known and are transmitted exclusively by specific insect vectors. Some are associated with highly diverse circular, ssDNA satellites that play a part in disease progression and provide evidence of the interaction of geminiviruses with other families of plant‐infecting viruses. Collectively, geminiviruses are pathogens of cereals, vegetable and fibre crops, posing a serious threat to agriculture worldwide. Efforts to control these viruses by conventional means have either proven unsuccessful or have not been durable. For this reason, researchers are increasingly looking to engineered resistance as a means to control these important viruses. This has recently led to the first crop with engineered resistance to a geminivirus reaching the field. Key Concepts Geminiviruses are important insect‐transmitted pathogens of cereal, vegetable and fibre crops in tropical and temperate regions throughout the world, including developed and developing countries. Geminiviruses often cause striking symptoms in plants, indeed the earliest description of virus symptoms in plants is believed to relate to those caused by a geminivirus and such symptoms occasionally are considered to be horticulturally desirable. All geminiviruses have single‐stranded DNA genomes and a twinned particle morphology that is unique to this family of plant viruses. Some geminiviruses are associated with single‐stranded DNA satellites, referred to as alpha‐ and betasatellites, the latter playing an essential role in maintenance of the disease. Because their small DNA genomes encode only a limited number of genes, geminiviruses manipulate the metabolism of the infected cell to produce conditions suitable for their proliferation. Geminiviruses are proving invaluable in the investigation of fundamental biological processes such as DNA replication, cell‐cycle regulation, gene expression and pathogen resistance in plants. Geminiviruses are highly recombinogenic, and the derivation of a large number of geminivirus and satellite DNA sequences is providing important insights into their diversity, adaptability and evolution. Conventional control strategies, such as the use of chemicals to eliminate their insect vectors and breeding natural host plant resistance, have proven ineffective in reducing crop losses to geminivirus infection, leading to the development of promising alternative (genetically engineered) strategies. Sequences derived from geminiviruses are being used to develop systems for high‐level expression of valuable proteins in plants.