Aureusvirus, a novel genus in the family Tombusviridae

Abstract

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.

Aureusvirus P14 Is an Efficient RNA Silencing Suppressor That Binds Double-Stranded RNAs without Size Specificity

“…To better understand the evolution of silencing suppression within Tombusviridae, we wanted to identify and analyze the silencing suppressor of Pothos latent virus (PoLV), the type species of aureusviruses (Tombusviridae). The genome organization of aureusviruses is identical to that of tombusviruses, but the Aureusvirus genome is significantly smaller and the sequence similarity between the two genera is limited (26,28,41) (Fig. 1A).…”

Characterization of a Virus from Pigeonpea with Affinities to Species in the Genus Aureusvirus, Family Tombusviridae

“…However, in serological tests, the virus reacted with antiserum to only 1 (PoLV) of 11 virus species in this family tested. PoLV is the type member of the newly proposed genus Aureusvirus of the family Tombusviridae (16,22). The PoLV-PP genome contains five ORFs and, although no in vitro translation studies were made in this study, the putative amino acid sequence deduced from the five ORFs showed 92 to 98% sequence similarity with PoLV (Table 3); therefore, the functional properties of the proteins expressed from these five ORFs are likely to be similar to those of PoLV (22)(23)(24).…”

“…The virus is shown to be very similar to PoLV and we therefore consider it to be a pigeonpea isolate of PoLV (PoLV-PP). PoLV-PP exhibited the characteristic features of species in the genus Aureusvirus of the family Tombusviridae, including the following: icosahedral particles, a single coat protein species of approximately 44 kDa, monopartite single-stranded RNA genome without a poly(A) tail, and encapsidation of 2 subgenomic RNAs (16). The genome of tombusviruses acts as an mRNA for the expression of the 5′ proximal genes (ORF1 and 2), but the 3′ genomic RNA is expressed via two 3′ coterminal subgenomic RNAs, and the encapsidation of subgenomic RNAs is reported for several tombusviruses (24).…”

Molecular and Serological Identification of Cucumber leaf spot virus in Iran

“…; Martelli et al. ) and through seeds (Weber ). CLSV is reported to elicit systemic mottling or chlorotic spots sometimes with a necrotic centre on older leaves (Weber et al.…”

“…CLSV was first identified in cucumber (C. sativus L.) in Germany (Weber et al 1982) and has since been reported from Greece, UK, Jordan (Weber 1986), Saudi Arabia, Spain (Segundo et al 2001) and Poland (Pospieszny et al 2004). Natural transmission of CLSV is by zoospores of the chytrid fungus Olpidium bornovanus (Campbell et al 1991;Martelli et al 1998) and through seeds (Weber 1986). CLSV is reported to elicit systemic mottling or chlorotic spots sometimes with a necrotic centre on older leaves (Weber et al 1982;Rosner et al 2006), and slight stunting and delay of flowering (Pospieszny et al 2004).…”