Aureusvirus , a novel genus in the family Tombusviridae
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Virology Division News Arch Virol 143/9 (1998)
1847
Virology Division News
Aureusvirus, a novel genus in the family Tombusviridae G. P. Martelli, M. Russo, L. Rubino, and S. Sabanadzovic Dipartimento di Protezione delle Piante, Università degli Studi and Centro di Studio del CNR sui Virus e le Virosi delle Colture Mediterranee, Bari, Italy
Summary. Aureusvirus is a new genus of plant viruses typified by pothos latent virus (PoLV) and comprising cucumber leaf spot virus (CLSV), previously classified as definitive species in the genus Carmovirus. Aureusviruses are soil-borne viruses readily transmitted by sap inoculation to a moderate range of hosts. Natural transmission of CLSV is by the chytrid fungus Olpidium bornovanus, whereas PoLV infects the host without the apparent intervention of a vector. Aureusviruses have isometric particles with size (c. 30 nm) and structure similar to those of the family Tombusviridae, to which the genus belongs. The genome consists of a molecule of single-stranded, positive-sense RNA c. 4.4 kb in size comprising five ORFs. The structural organization (i.e. number and order of genes) is virtually identical to that of members of the genus Tombusvirus. However, the aureusvirus genome has a smaller size and shows distinct differences in the amino acid sequence of some of the ORFs. ORF 1 encodes a 25 kDa product and terminates with a leaky amber codon the readthrough of which results in a 84 kDa protein (ORF 2) with the conserved motifs of RNA dependent RNA polymerase. ORF 3 encodes the coat protein (40–41 kDa), ORF 4 the movement protein (27 kDa), and ORF 5 a 14–17 kDa product responsible for symptom severity. Virions accumulate in great quantity in the cytoplasm, often forming crystalline aggregates, and in bubble-like evaginations of the tonoplast protruding into the vacuole. Replication is likely to occur in the cytoplasm with a stategy based on direct expression of the 5' proximal ORF and expression of downstream ORFs through subgenomic RNAs. Introduction Pothos latent virus (PoLV), a virus with isometric particles c. 30 nm in diameter and a positive-sense single-stranded RNA genome, was isolated by mechanical inoculation from symptomless plants of Scindapsus aureus (pothos) in Southern Italy [11]. PoLV has biological (host range reactions) and epidemiological properties (vectorless transmission through the soil) resembling those of members of the family Tombusviridae, and is serologically distantly related to species of the genera Carmovirus and Tombusvirus. However, the physicochemical properties are sufficiently different from those of tombusand carmoviruses to make the classification of PoLV uncertain [11]. Sequencing and
Virology Division News
1848
molecular analysis of PoLV RNA revealed that the virus has genome structure and organization virtually identical to that of tombusviruses but differs in size (4.4 kb versus 4.7 kb) and in the sequence of some of the ORFs [6, 7]. The cytopathology of PoLV infections is also quite different from that of tombusviruses [10, 11], st
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