Aphis citricidus bunyavirus (AcBV) is assigned to Citricivirus chongqinense, the only species in the genus. Citricivirus RNA has been found by high-throughput sequencing of RNA from a brown citrus aphid [Toxoptera citricida (Kirkaldy, 1907)] from Chongqing (重庆市), China. The citricivirus genome has four genes, encoding a large protein (L), two external glycoproteins (Gn and Gc) and a nucleocapsid protein (N). Based on well-supported Maximum Likelihood or Maximum Clade Credibility trees inferred from complete L protein sequences, viruses classified in the genus Citricivirus form a monophyletic cluster clearly distinguished from other phenuivirids. There currently is no cultured citricivirus isolate (Zhang et al., 2019).
Virion morphology is unknown. Based on the putative proteins encoded by the virus genome, the virion is probably spherical or pleomorphic and enveloped.
Nucleic acid and Protein
Citricivirus genomes encompass three segments of negative-sense RNA: L (6.9 kb), M (4.2 kb) and S (1.2 kb). Analysis of the terminal sequences has yet to be completed. 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 virus-complementary strand. In silico analysis of the citricivirus putative ORF sequences suggests that citricivirus encodes three structural proteins: L with a predicted molecular mass of 255 kDa, a glycoprotein precursor (GP) of 140 kDa and N of 31 kDa, these protens sharing sequence homology and/or structural characteristics with the cognate proteins of other phenuivirids (Zhang et al., 2019).
Genome organization and replication
Citricivirus genome arrangement is similar to that of beidiviruses, goukoviruses, hudiviruses, hudoviruses, phasiviruses, pidchoviruses, and tanzaviruses (Figure 1.Citricivirus). The L, M and S segments putatively encode L, a glycoprotein precursor (comprising Gn and Gc) and N, respectively. The Gn and Gc glycoproteins of 56 kDa and 57 kDa were earlier referred to as G1 and G2 based on apparent size on gel electrophoresis, respectively. The citricivirus genome does not encode either of the non-structural proteins NSs or NSm. Details of virus replication are unknown (Zhang et al., 2019).
|Figure 1. Citricivirus. Genome organization of a citricivirus. Coloured boxes depict ORFs that encode N, nucleocapsid protein; Gn and Gc, external glycoproteins; and L, large protein.|
The only known virus was detected in a brown citrus aphid [Toxoptera citricida (Kirkaldy, 1907)](Zhang et al., 2019).
Species demarcation criteria
Not defined as the genus currently includes only a single species.