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 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.

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To direct the genome synthesis, RNA viruses without a DNA stage in the replication cycle use RNA-dependent RNA polymerase (RdRp). All RdRps have conserved right hand-like shape that includes characteristic A-->B-->C sequence motifs forming the active site. Recently, the structural permutation of the RdRp active site (C-->A-->B) has been described in few double-stranded RNA birnaviruses and a subset of positive-stranded RNA tetraviruses distantly related to Picorna-like viruses. Here we describe a permuted RdRp in the newly identified plant alpha-like virus with 6.5 kb-long polyadenylated genome, dubbed Grapevine virus Q (GVQ). The multi-domain layout and sequence similarities place GVQ into the genus Marafivirus of the family Tymoviridae. In contrast to other tymovirids, GVQ has 21 amino acid residues corresponding to the motif C relocated upstream of the motif A in the putative RdRp. This unique sequence characteristic was extensively verified and identified in several GVQ isolates infecting wild and cultivated Vitis and Rubus spp.

The complete nucleotide sequence of Grapevine fleck virus (GFkV) genomic RNA was determined. The genome is 7564 nt in size, excluding the 3h-terminal poly(A) tail, is characterized by an extremely high cytosine content (ca. 50 %), and contains four putative open reading frames and untranslated regions of 291 and 35 nt at the 5h and 3h ends, respectively. ORF 1 potentially encodes a 215n4 kDa polypeptide (p215), which has the conserved motifs of replication-associated proteins of positive-strand RNA viruses. ORF 2 encodes a 24n3 kDa polypeptide (p24) identified as the coat protein. ORFs 3 and 4 are located at the extreme 3h end of the viral genome and encode proline-rich proteins of 31n4 kDa (p31) and 15n9 kDa (p16), respectively, of unknown function. Phylogenetic analysis of the viral replicase and coat protein genes showed that GFkV is related to members of the Tymovirus and Marafivirus genera. Two subgenomic RNAs were present in the GFkV preparations as ascertained by molecular hybridization. The genome organization of GFkV resembles to some extent that of tymoviruses and marafiviruses. However, differences in the biological and epidemiological behaviour, cytopathology and molecular properties (i.e. size of genomic RNA and coat protein, and number of ORFs) support the notion that GFkV is a separate virus belonging in a new genus.