N. Abou Ghanem-Sabanadzovic

Maculavirus, a new genus of plant viruses

Summary.Maculavirus is a new genus of plant viruses typified by Grapevine fleck virus (GFkV). A possible second member is Grapevine redglobe virus (GRGV). Maculaviruses are phloem-limited non-mechanically transmissible viruses with isometric particles c. 30 nm in diameter that have a rounded contour and prominent surface structure. Vectors, if any, are unknown. GFkV preparations contain two centrifugal components, T made up of empty protein shells and B, which contains 35% RNA. The coat protein (CP) has a molecular mass of 24 kDa. The genome is a single-stranded RNA that has c. 50% cytosine residues. It is 7564 nt in size, excluding the poly(A) tail and contains four putative open reading frames (ORF) that encode a 215.4 kDa polypeptide with the conserved motifs of replication-associated proteins of positive-strand RNA viruses (ORF1), the CP (ORF2), and one (GRGV) or two (GFkV) proline-rich polyproteins of 31.4 kDa (ORF3) and 15.9 kDa (ORF4), respectively, with unknown function. Replication-associated proteins and CP are phylogenetically related to those of members of the genera Tymovirus and Marafivirus. GFkV-infected grapevine cells contain vesiculated mitochondria, the possible site of RNA replication. In the natural host, GFkV particles accumulate in great quantity, sometimes in crystalline arrays in phloem cells.

A novel monopartite dsRNA virus from rhododendron

A dsRNA molecule of 3.4 kbp was extracted from two great rhododendron samples from Great Smoky Mountains National Park. Sequencing of this molecule suggests that it represents the genome of an undescribed virus, for which the provisional name rhododendron virus A (RhVA) is proposed. In phylogenetic analyses, this virus clustered together with southern tomato virus and related viruses, forming a coherent and distinct clade among dsRNA viruses. RhVA likely belongs to a yet-to-be-established taxon of viruses with a non-segmented dsRNA genome.