Tymoviruses

Authors: Hammond, Rosemarie; Abrahamian, Peter

Submitted to: Encyclopedia of Virology
Publication Type: Book / Chapter
Publication Acceptance Date: 1/13/2020
Publication Date: 2/24/2021
Citation: Hammond, R., Abrahamian, P. 2021. Tymoviruses. Encyclopedia of Virology. 3:818-826. https://doi.org/10.1016/B978-0-12-809633-8.21305-8.
DOI: https://doi.org/10.1016/B978-0-12-809633-8.21305-8

Interpretive Summary: The field of virology has advanced significantly thanks to new technologies and in response to viral outbreaks, however, valuable descriptive resources, including the Encyclopedia of Virology, have not been updated for several years. In plants, several members of the tymovirus family of plant viruses cause major diseases in several crops, including grains, vegetable, citrus, grapevine, and tree fruits, some of which have been only recently described. This comprehensive overview of the tymoviruses is intended as a major reference work that will be of value to an international audience of researchers in industry, academia, and government organizations with an interest in plant pathology and virology and the control of plant diseases.

Technical Abstract: The family Tymoviridae is comprised of the genera Tymovirus, Marafivirus, and Maculavirus, and two unassigned species. All these viruses have ~29 nm nonenveloped T = 3 icosahedral particles. Infectious ‘bottom component’ virions and noninfectious, empty ‘top component’ capsids are produced. The 5'-capped monopartite positive-stranded RNA genomes are 6–7.5 kb long, and most of each genome encodes a long replication protein (RP) with methyltransferase, papain-like proteinase, helicase, and RNA-dependent RNA polymerase (RdRp) motifs. The RP is processed by cleavage between the helicase and RdRp domains. Tymovirus genomes have an extensively overlapping open reading frame (ORF) encoding a protein that is necessary for cell-to-cell movement and that suppresses the host RNA interference response. All tymoviruses produce 3' subgenomic RNAs that allow expression of the coat protein (CP). The marafiviruses produce a second, larger variant of the CP by cleavage from the RP/CP precursor. Most tymovirus genomes have a valine-specific tRNA-like structure at the 3' end. Tymoviruses amplify to high yields, and are transmissible mechanically and by beetles over short distances. Members of the genera Marafivirus and Maculavirus are phloem-limited and not mechanically transmissible. The grass-infecting marafiviruses are transmitted by leafhoppers, in a persistent-propagative manner, the insect supporting viral replication.