Family: Phenuiviridae

Genus: Entovirus

Distinguishing features

Five viruses are assigned to the genus Entovirus. Entovirus RNA has been detected by high-throughput sequencing of RNA from a fungus of the genus Entoleuca and by soil metagenome analysis. The entovirus genome has three genes, encoding two structural proteins, a large protein (L) and a nucleocapsid protein (N), and one non-structural gene likely encoding a viral movement protein (MP) that enables cell-to-cell movement in fungal hosts. The apparent lack of a membrane-bound virus particle distinguishes entoviruses 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 Entovirus form a monophyletic cluster clearly distinguished from other phenuivirids (Velasco et al., 2019, Chen et al., 2022).

Virion

Morphology

Virion morphology is unknown.

Nucleic acid

The entovirus genome consists of two single-stranded RNA segments: RNA1 (7.3–8.1 kb) and RNA2 (2.5–3.1 kb). The terminal nucleotides of each segment occur in a canonical, conserved sequence (in coding sense) 5′-ACACAAAGAC… GUCUUUGUGU-3′ that may form panhandle structures typical of other members of the class Bunyaviricetes. In silico analysis of entovirus putative ORF sequences suggests that the entovirus genome encodes two proteins with predicted molecular masses of 271.4–298.5 kDa and 36.6–40.6 kDa that share homology with the bunyaviral RNA-directed RNA polymerase (RdRP) domain and the tenuivirus/phlebovirus N domain, respectively, and one predicted protein of 39.1–50.3 kDa that shares sequence homology and/or structural characteristics with the MP of plant viruses (Velasco et al., 2019).

Genome organization and replication

The entovirus genome consists of two negative-sense and ambisense RNAs (Figure 1 Entovirus). The entovirus genome arrangement is similar to that of coguviruses and lentinuviruses (Figure 2 Phenuivridae). The entovirus genome encompasses two segments of negative-sense RNA: RNA1, encoding the L protein that is the putative RdRP, and the ambisense RNA2, which is transcribed by RdRP to form a subgenomic virus-complementary mRNA that encodes N from a viral antigenome RNA2, and also transcribed to form a subgenomic virus-sense mRNA that encodes MP from a viral genome RNA2. The two ORFs on RNA2 are separated by a noncoding intergenic region that potentially forms a long A/U rich stem-loop structure. Since most plant viruses encode viral suppression proteins that counteract plant antiviral defence mechanisms based on RNA silencing, one or more of the proteins encoded by entoviruses may interfere with RNA silencing. Details of virus replication are unknown (Velasco et al., 2019, Rodriguez Coy et al., 2022).

Figure 1 Entovirus. Genome organization of an entovirus. 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

Entoviruses have been identified from a fungus of the genus Entoleuca obtained from the rhizosphere of avocado in Spain and from soil-derived metagenomic datasets obtained in China. (Velasco et al., 2019).

Species demarcation criteria

The criteria demarcating species in the genus are:

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

Related, unclassified viruses

* Sequences do not comprise the complete genome segment.

Virus names and virus abbreviations are not official ICTV designations.