Family: Phenuiviridae

Genus: Rubodvirus

Distinguishing features

Four viruses are assigned to the genus Rubodvirus. Rubodviruses were identified first in apple and later in grapevine, pear and quince. The rubodvirus genome has three genes, encoding a large protein (L), a nucleocapsid protein (N) and a putative viral movement protein (MP) that may enable cell-to-cell movement in plant hosts. The apparent lack of a membrane-bound virus particle distinguishes rubodviruses from other viruses in the family Phenuiviridae. Based on well-supported Maximum Likelihood or Maximum Clade Credibility trees inferred from complete L protein sequences, viruses classified in the genus Rubodvirus form a monophyletic cluster clearly distinguished from other phenuivirids (Rott et al., 2018, Diaz-Lara et al., 2019).

Virion

Virion morphology is unknown.

Nucleic acid

The rubodvirus genome encompasses three segments of negative-sense RNA: RNA1 (7.2–8.1 kb), RNA2 (1.5–1.6 kb), and RNA3 (1.3–1.6 kb). The terminal nucleotides of each segment occur in a canonical, conserved sequence (in coding sense) 5′-ACCCCUCCAA…UGGAGGGGGU-3′ and may form panhandle structures typical of other members of the class Bunyaviricetes. All three genomic RNAs contain untranslated regions flanking a single ORF which, based on comparisons with other negative-sense RNA viruses, is predicted to be contained in the viral complementary strand. In silico analysis of rubodvirus putative ORF sequences suggests that rubodviruses encode two structural proteins: L with a predicted molecular mass of 275.6–307.1 kDa that is homologous with the bunyaviral RNA-directed RNA polymerase (RdRP) domain, and N of 32.2–32.4 kDa that is homologous with the tenuivirus/phlebovirus N domain, as well as one non-structural protein of 43.6–45.1 kDa that is homologous with and/or shares structural characteristics with the MP of other viruses (Rott et al., 2018, Diaz-Lara et al., 2019).

Genome organization and replication

The rubodvirus genome consists of three negative-sense RNAs (Figure 1 Rubodvirus). The rubodvirus genome arrangement is similar to that of bociviruses and laulaviruses (Figure 2 Phenuivridae). These segments putatively encode L, MP and N, respectively. Most plant viruses encode viral suppressor proteins that counteract plant antiviral defense mechanisms through RNA silencing. There is a possibility that one or more of the three proteins encoded by rubodviruses may interfere with RNA silencing. Multifunctional roles have been reported for viral suppressor proteins of other viruses (Rott et al., 2018, Diaz-Lara et al., 2019, Kormelink et al., 2021).

Figure 1 Rubodvirus. Genome organization of a rubodvirus. Coloured boxes depict ORFs that encode N, nucleocapsid protein and L, large protein. A white box depicts an ORF that encodes MP, non-structural cell-to-cell movement protein.

Biology

Hosts of rubodviruses are plants of the families Vitaceae: grapevine [Vitis vinifera (L.,1758)] and Rosaceae: apple [Malus domestica (Suckow) Borkh., 1803)], pear [Pyrus pyrifolia ((Burm.f.) Nakai, 1926)], and quince [Cydonia oblonga (Mill, 1768)]. Viruses are transmitted by grafting (McCrum et al., 1960, Rott et al., 2018, Diaz-Lara et al., 2019).

Species demarcation criteria

The criteria demarcating species in the genus is:

•　Less than 95% identity in the amino acid sequence of the L protein.

Related, unclassified viruses

Virus names and virus abbreviations are not official ICTV designations.