Genus: Dichorhavirus


Genus: Dichorhavirus

Distinguishing features

Viruses assigned to the genus Dichorhavirus form a monophyletic group based on well-supported Maximum Likelihood trees inferred from complete L sequences. Dichorhaviruses produce short bacilliform virions that lack a clearly distinguishable lipid envelope and have bi-segmented genomes. They share several characteristics with nucleorhabdoviruses, such as nuclear viroplasm, cytopathological effects in the nucleus, composition of structural proteins and gene order, sequence similarity and transcription mechanism. They are transmitted by false spider mites (genus Brevipalpus) in which they appear to replicate.

Virion

Morphology

Dichorhaviruses produce short, bacilliform virions, 40 × 100–110 nm in size. Virions appear not to be enveloped but may be found in association with host membranes (Kitajima et al., 2003, Kondo et al., 2009). 

Nucleic acid

The negative-sense single-stranded RNA genome is bi-segmented. RNA 1 (6.4–6.6 kb) contains five genes and RNA 2 (6.0 kb) contains a gene coding for L (Kondo et al., 2006, Ramalho et al., 2014). The termini of each segment are complementary and all genes are separated by conserved intergenic regions. Anti-genomic (positive-sense) RNAs are also present as a minor component (10–20 %) in purified orchid fleck virus (OFV) virions (Kondo et al., 2009).

Proteins

Dichorhaviruses express the five canonical rhabdovirus structural proteins, nucleocapsid protein (N), phosphoprotein (P), matrix protein (M) and glycoprotein (G) and RNA polymerase (L). N, G and L have moderate to high sequence similarity with the cognate proteins of nucleorhabdoviruses. The P3 protein is a putative movement protein (Kondo et al., 2006, Ramalho et al., 2014).  In OFV, the masses of the proteins are 49 kDa (N), 26 kDa (P), 38 kDa (P3), 20 kDa (M), 61 kDa (G) and 212 kDa (L).

Genome organisation and replication

The genome organisation of viruses in the genus Dichorhavirus resembles that of plant-infecting rhabdoviruses in the genera Cytorhabdovirus and Nucleorhabdovirus, except that the RNA genome occurs as two segments: RNA 1 contains genes encoding five proteins in the order 3′-N-P-P3-M-G-5′ and RNA 2 codes for L (Figure 1.Dichorhavirus). Replication and transcription mechanisms closely resemble those reported for nucleorhabdoviruses.

Figure 1.Dichorhavirus. Schematic representation of dichorhavirus genome segments (RNA1 and RNA2). N, P, M, G and L represent ORFs encoding the structural proteins. ORF 3, encoding the putative viral cell-to-cell movement protein gene, is highlighted (blue). 

Biology

Dichorhaviruses are transmitted by false spider mites of the genus Brevipalpus (Arthropoda: Arachnida: Acari: Tenuipalpidae) in which they also probably replicate (Kitajima et al., 2003, Chagas et al., 2003, Kitajima and Alberti 2014, Kondo et al., 2003, Roy et al., 2015). Dichorhavirus infections lead to local chlorotic and/or chlorotic spots on leaves and fruits (and/or systemic symptoms in some cases). OFV infection is characterised by typical cytopathic effects in the nuclei of infected cells (Kitajima et al., 2001, Chang et al., 1976). OFV has a global distribution and infects orchids and other ornamentals (such as lilyturf) (Peng et al., 2013, Mei et al., 2016). Strains of OFV infecting citrus with >90% nucleotide sequence identity have been reported and their occurrence may be geographically constrained. In addition, strains of a novel unclassified dichorhavirus, citrus leprosis virus N, were recently identified infecting citrus species in the Americas (Ramos-Gonzalez et al., 2017). Coffee ringspot virus (CoRSV) has been reported to infect coffee in South America and its genetic variability and epidemiology has been studied (Ramalho et al., 2016).

Species demarcation criteria

Viruses assigned to different species within the genus Dichorhavirus have a minimum nucleotide sequence divergence of 25% in the L gene (Dietzgen et al., 2014).

Member Species

SpeciesVirus name(s)Exemplar isolateExemplar accession numberExemplar RefSeq numberAvailable sequenceOther isolatesOther isolate accession numbersVirus Abbreviation(s)Isolate Abbreviation
Coffee ringspot dichorhaviruscoffee ringspot virusLavrasRNA1: KF812525; RNA2: KF812526Complete genomeCoRSV
Orchid fleck dichorhavirusorchid fleck virusSoRNA1: AB244417; RNA2: AB244418RNA1: NC_009608; RNA2: NC_009609Complete genomeOFV

Virus names, the choice of exemplar isolates, and virus abbreviations, are not official ICTV designations.
Download GenBank/EMBL query for sequences listed in the table here.

Derivation of names

Dichorhavirusfrom the bi-segmented characteristic of the viral genomes (Dicho: from Greek, meaning “in two, apart or asunder”).

Related, Unclassified Viruses 

Virus name

Accession number

Virus abbreviation

citrus chlorotic spot virus

KY700685, KY700686

CiCSV

citrus leprosis virus N

KY751404, KY751405

CiLV-N

Clerodendrum chlorotic spot virus

HQ853700

ClCSV

Virus names, the choice of exemplar isolates, and virus abbreviations, are not official ICTV designations.
Download GenBank/EMBL query for sequences listed in the table here.