Subfamily: Betarhabdovirinae
Genus: Deltanucleorhabdovirus
Distinguishing features
Historically, the genera Nucleorhabdovirus and Cytorhabdovirus were established based on the sites of virus replication and morphogenesis, with nucleorhabdoviruses replicating and maturing in the nuclei of infected cells. Recently, a reclassification became necessary as phylogenetic analyses of new plant rhabdovirus genomes consistently showed that nucleorhabdoviruses did not form a monophyletic clade based on well-supported Maximum Likelihood or Maximum Clade Credibility trees inferred from complete L sequences complete L protein sequence alignments (Kuhn et al., 2020).
Medicago sativa virus 1 (MSV1; species Deltanucleorhabdovirus medicagonius) and strawberry virus 3 (StrV3, species Deltanucleorhabdovirus fragariae) are the only members of the genus Deltanucleorhabdovirus. MSV1 and StrV3 cluster together in a distinct clade that is basal to alpha-, beta- and gammanucleorhabdoviruses. Moreover, nucleotide and deduced amino acid sequence comparisons between them, as well as between MSV1 and StrV3 and other plant rhabdoviruses, are extremely low.
Virion
Morphology
Virions are likely to be similar to those reported for alpha-, beta- and gammanucleorhabdoviruses.
Nucleic acid
The negative-sense, single-stranded RNA genome of 14.4 kb is unsegmented.
Proteins
All StrV3 proteins were predicted to contain nuclear localization signals (NLS), except P3 (Medberry et al., 2023).
Lipids
The lipoprotein envelope is derived from the host plant or insect vector (Jackson et al., 2005a). Lipid composition is unknown.
Genome organisation and replication
The StrV3 genome (14.4 kb) has the gene order 3′-N-P-P3-M-G-L-5′- similar to that of the betanucleorhabdovirus Sonchus yellow net virus (SYNV; species Betanucleorhabdovirus retesonchi) (Medberry et al., 2023) (Figure 1 Deltanucleorhabdovirus). The MSV1 genome is also similar.
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| Figure 1 Deltanucleorhabdovirus. Schematic representation of deltanucleorhabdovirus genomes shown in reverse (positive-sense) polarity. N, P, M, G and L represent ORFs encoding the structural proteins. ORF3 encoding the putative viral cell-to-cell movement protein is highlighted (blue). |
Biology
StrV3 was identified in strawberry; while MSV1 was identified in alfalfa. StrV3 was not able to be transmitted by the strawberry aphid (Medberry et al., 2023).
Species demarcation criteria
Viruses assigned to different species within the genus Deltanucleorhabdovirus have several of the following characteristics: A) nucleotide sequence identity lower than 75% in the complete genome sequence; B) occupy different ecological niches as evidenced by differences in hosts and/or arthropod vectors; and C) can be clearly distinguished in serological tests or by nucleic acid hybridization.