Proposed classification of the bipartite-genomed raspberry bushy dwarf idaeovirus, with tripartite-genomed viruses in th
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Proposed classification of the bipartite-genomed raspberry bushy dwarf idaeovirus, with tripartite-genomed viruses in the family Bromoviridae A. Ziegler,M. A. Mayo, and A. F. Murant Scottish Crop Research Institute, Invergowrie, Dundee, Scotland
Summary. Raspberry bushy dwarf virus (RBDV) has an unusual combination of properties and has been classified as the sole member of a new plant virus genus, for which the name idaeovirus has been proposed. Particles of RBDV resemble those of ilarviruses (family Bromoviridae) in appearance and in being transmitted in association with pollen. RBDV has two genomic RNA species, RNA-1 (5 449nt) and RNA-2 (2231 nt). The particles also contain RNA-3 (946 nt), a subgenomic monocistronic coat protein mRNA which is derived from the 3' end of the bicistronic RNA-2. The single 190 K protein encoded by RNA-1 contains methyltransferase, helicase and polymerase domains. Evolutionary distance data obtained from multiple alignments of the amino acid sequence of the RBDV 190 K protein and corresponding proteins with replicative function from other plant viruses suggest that the closest affinities of RBDV are with the tripartite genomed viruses in the family Bromoviridae. We propose that the genus idaeovirus be included in the family Brornoviridae.
Introduction Raspberry bushy dwarf virus (RBDV) has an unusual combination of properties which distinguishes it from all plant viruses for which taxonomic descriptions are published [12]. It has therefore been classified as the sole member of a new plant virus genus, for which the name idaeovirus has been proposed to the International Committee for the Taxonomy of Viruses [30]. RBDV is transmitted in association with pollen [28, 29] and has isometric particles about 33 nm in diameter which are easily deformed when prepared for electron microscopy. RBDV particles contain three RNA species, of which RNA-1 (5 449 nt) [36] and RNA-2 (2 231 nt) [31] comprise the genome. RNA-3 (946 nt) [26] is a subgenomic monocistronic mRNA for the coat protein and is derived from the 3' end of the bicistronic RNA-2. The Y-most open reading frame (ORF) of RBDV RNA-2 encodes a 39 K protein [31] which has a slight sequence similarity (see below) to the putative
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transport protein of alfalfa mosaic alfamovirus (A1MV), which is itself encoded by the 5'-most gene of the bicistronic RNA-3 (2055nt) of A1MV [3]. The subgenomic mRNA for the A1MV coat protein (RNA-4:881 nt) [4] is a 3'coterminal derivative of A1MV RNA-3. RNA-2 and RNA-3 of RBDV are therefore similar in size and genetic organization to RNA-3 and RNA-4, respectively, of A1MV and of other viruses in genera proposed to comprise the family Bromoviridae [24]. However, the bipartite nature of the RBDV genome and the size of its RNA-1 distinguish it from these viruses. RBDV RNA-1 contains a single large ORF [36] encoding a 190 K protein that contains methyltransferase, helicase and polymerase domains typical of viral proteins with replicative funct
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