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The family Tymoviridae
G P Martelli1, S Sabanadzovic, N Abou-Ghanem Sabanadzovic
1Dipartimento di Protezione delle Piante e Microbiologia Applicata, Università degli Studi and Istituto di Virologia Vegetale del CNR, Bari, Italy.
Abstract:
The family Tymoviridae comprises the genus Tymovirus, from which it derives its name, the genus Marafivirus and the newly established genus Maculavirus. Members of the family share the following characteristics: (i) non-enveloped isometric particles c. 30 um in diameter, with a rounded contour and prominent surface structures, and clustering of coat protein subunits in pentamers and hexamers; (ii) the presence in preparations of purified virus particles of two centrifugal components, made up of non-infectious protein shells (T) that may contain small amounts of RNA (primarily subgenomic coat protein mRNA) and of infectious nucleoproteins (B), that contain the virus genome; (iii) possession of a positive-sense, single-stranded RNA genome with an unusually high cytidine content (32 to c. 50%), capped at the 5' terminus and containing a very large ORF encodes replication-related proteins analogous to those of other taxa of the "alpha-like" supergroup of ssRNA viruses; (iv) a replication strategy possibly encompassing posttranslational proteolytic cleavage of the polypeptide encoded by ORF1 by a papain-like virus-encoded protease, and coat protein expression via a subgenomic RNA; (v) the presence in infected cells of cytopathic structures, thought to be the sites of RNA replication, originating from severely altered chloroplasts and/or mitochondria, the periphery of which is lined with vesicles produced by the localized invaginations of the bounding membrane. There are 23, 4, and 2 known species in the genera Tymovirus, Marafivirus and Maculavirus, respectively. The genus Marafivirus also contains one tentative species.
Insights
The Tymoviridae family includes Tymovirus, Marafivirus, and Maculavirus genera, characterized by specific viral particle structures and RNA genomes. These viruses replicate within altered plant organelles, forming unique cytopathic structures.
Area of Science:
- Virology
- Plant Pathology
- Molecular Biology
Background:
- The family Tymoviridae encompasses three genera: Tymovirus, Marafivirus, and Maculavirus.
- Tymoviridae viruses share common characteristics including non-enveloped isometric particles and positive-sense single-stranded RNA genomes.
Purpose of the Study:
- To describe the defining characteristics of the Tymoviridae family, including its genera and viral properties.
- To detail the structural, genomic, and replication strategies of Tymoviridae members.
Main Methods:
- Characterization of viral particle morphology and composition.
- Analysis of viral genome structure and gene expression strategies.
- Investigation of virus-induced cytopathic effects in host cells.
Main Results:
- Tymoviridae particles are non-enveloped, isometric (approx. 30 µm), with distinct surface structures and protein subunit arrangements.
- Viral genomes are positive-sense, single-stranded RNA with high cytidine content, capped 5' terminus, and a large ORF encoding replication proteins.
- Replication involves posttranslational cleavage and coat protein expression via subgenomic RNA, with replication occurring in altered chloroplasts/mitochondria.
Conclusions:
- The Tymoviridae family is defined by specific structural and genomic features, including unique replication mechanisms.
- Viral replication leads to the formation of characteristic cytopathic structures derived from host organelles.
- The family comprises 23 Tymovirus, 4 Marafivirus, and 2 Maculavirus species, with one tentative Marafivirus species.