A fourth RNA with no apparent messenger activity, and which is slightly smaller than the RNA3, is encapsidated (Martelli and Grieco 1997).
Virions range from quasi-spherical with a diameter of 26 nm, to bacilliform with lengths of 37, 43, 38, and 55 nm, and diameters of 18 nm. Particles up to 85 nm in length occasionally are present (Figure 1D.Bromoviridae).
Physicochemical and physical properties
In sucrose gradients, virions sediment as five or six components.
Virions encapsidate the three genomic RNAs as well as a fourth RNA species of about 2 kb, that is apparently not an mRNA. The subgenomic RNA for the coat protein (CP) ORF is not encapsidated. Three additional RNAs of 200 to 550 nt are also present in virions. The 5′-termini of the genomic RNAs are capped, but not the 5′-terminus of the encapsidated sgRNA. The 3′-termini of the RNAs are similar to those of viruses belonging to the genera Alfamovirus and Ilarvirus, but do not interact with CP to activate replication.
Virions contain a CP of 24 kDa.
Genome organization and replication
The genome is organized as depicted in Figure 2A.Bromoviridae and consists of three functional molecules of 3126 nt (RNA1, monocistronic), 2734 nt (RNA2, monocistronic), and 2438 nt (RNA3, bicistronic). Virions encapsidate a fourth RNA of 2078 nt (RNA4) with no apparent messenger activity. The strategy of replication includes proteolytic processing and subgenomic RNA production (Martelli and Grieco 1997). Oleavirus RNAs do not have a straightforward relationship with those of members of any of the current genera in the Bromoviridae, the closest homologue depending on which virus RNA is being compared.
Olive latent virus 2 (OLV2) has been recorded in southern Italy in olive and on the Aegean Greek islands of Rodi and Kastellorizo on castor bean (Ricinus communis). Infections are asymptomatic in olive whereas castor bean plants show yellowish vein netting and mottling of the leaves (Grieco et al., 2002). The virus is transmitted by mechanical inoculation, but no insect vector is known.
Virions are efficient immunogens.
Species demarcation criteria
Not applicable as there is only a single species in the genus.