Geminiviridae

Abstract

The Geminiviridae comprise a group of plant viruses with small, circular, single‐stranded deoxyribonucleic acid (DNA) 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, single‐stranded DNA betasatellites that are essential for disease progression. Their association with alphasatellites provides 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, such as using insecticides against their insect vectors and by breeding resistance, 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 diseases. 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 alphasatellites 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.

Self-Assembly of Viral Capsid Protein and RNA Molecules of Different Sizes: Requirement for a Specific High Protein/RNA Mass Ratio

“…the higher-order multiplets in the present study appeared to be aggregates of virus and proteinaceous material. The doublet structures have the superficial appearance of geminiviruses (50), which often form triplets and quadruplets (11). In the case of the African cassava mosaic geminiviruses containing defective interfering ssDNA, the number of multiplets increases with DNA length (21).…”

Seed Transmission of Tomato Leaf Curl New Delhi Virus from Zucchini Squash in Italy

“…For many years, begomoviruses have been unable to be transmitted by virus-infected seeds and were only transmitted by whitefly B. tabaci-mediation, grafting, and artificial inoculation with infectious clones [22]. However, according to recent reports, the following begomoviruses have shown seed-transmissible characteristics: sweet potato leaf curl virus, mung bean yellow mosaic virus, tomato yellow leaf curl virus, bitter gourd yellow mosaic virus, and dolichos yellow mosaic virus [23][24][25][26][27][28][29].…”

Peptide Aptamers That Bind to Geminivirus Replication Proteins Confer a Resistance Phenotype to Tomato Yellow Leaf Curl Virus and Tomato Mottle Virus Infection in Tomato

“…As a consequence, coupling the peptide aptamer strategy with existing resistance technologies with inherent specificity constraints provides a mechanism to extend the value of these technologies. For example, the success of creating resistant cultivars by conventional breeding has been limited because the resistance can be broken by the appearance of a recombinant virus or by an unfavorable environment where many viruses are present (17). Combining the peptide aptamers with conventional resistance would combat new geminivirus species or variants while maintaining conventional resistance against known viruses.…”

“…Conventional breeding has improved the productivity of some crops but has been limited by few sources of natural resistance, the multigenic nature of the resistance traits, and the time required for a breeding program (15,16). Resistance created by conventional breeding can be broken by the appearance of a recombinant virus, association with a DNA satellite, or an unfavorable environment where many viruses are present (17). Several transgenic strategies based on viral sequences have been evaluated, including microRNAs (18), antisense RNAs, RNA interference (RNAi) constructs, and mutant viral proteins (8).…”