The family Tymoviridae
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Virology Division News Arch Virol 147/9 (2002)
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Virology Division News
The family Tymoviridae G. P. Martelli1, S. Sabanadzovic2, N. Abou-Ghanem Sabanadzovic2, M. C. Edwards3, and T. Dreher4 1
Dipartimento di Protezione delle Piante e Microbiologia Applicata, Università degli Studi and Istituto di Virologia Vegetale del CNR, Bari, Italy 2 Istituto Agronomico Mediterraneo, Valenzano (Bari), Italy 3 USDA-ARS Cereal Crop Research Unit, Northern Crop Science Laboratory, Fargo, North Dakota, U.S.A. 4 Department of Microbiology, Oregon State University, Corvallis, Oregon, U.S.A.
Summary. 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 nm 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. Introduction Tymovirus [6], Marafivirus [7], and Maculavirus [15] are three plant virus genera that have the following traits in common: appearance, structural organization, and physicochemical properties of virus particles, a monopartite single-stranded RNA genome with a very high cytidine content, peripheral vesiculation of chloroplasts and/or mitochondria in infected cells, and similar genome organizations. Most of these properties seem to be specific to
Virology Division News
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these genera, so as to differentiate them from other plant virus taxa, and represent useful characters for defining a higher taxon. Furthermore, phylogenetic analysis of the coat protein (CP) and polymerase (RdRp) genes showed that the three genera are related. In these trees, members of these genera form three distinct clusters [16]
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