Family: Phenuiviridae

Genus: Fusavirus

Distinguishing features

Three viruses are assigned to the genus Fusavirus. Fusaviruses have been identified in plant-pathogenic fungi. The fusavirus genome consists of three single-stranded RNA segments, two negative-sense and one ambisense. Collectively, these segments encode the canonical phenuivirid structural proteins, designated a large protein (L), a glycoprotein precursor (GP), and a nucleocapsid protein (N), and one non-structural protein (NSs) of unknown function. Based on well-supported Maximum Likelihood or Maximum Clade Credibility trees inferred from complete L protein sequences, viruses classified in the genus Fusavirus form a monophyletic cluster clearly distinguished from other phenuivirids (Marzano et al., 2016, Navarro et al., 2018a, Navarro et al., 2018b, Nerva et al., 2019, Huang et al., 2023).

Virion

Morphology

Virion morphology is unknown.

Nucleic acid

The fusavirus genome comprises three single-stranded RNA segments, two negative-sense and one ambisense, designated L (6.4–7.8 kb), M (2.6–3.0 kb), and S (1.2–1.4 kb). The terminal sequences of these genomic segments have yet to be fully characterised. The L segment encodes a protein with a predicted molecular mass of 237.4–295.2 kDa that contains conserved domains characteristic of bunyaviral RNA-directed RNA polymerase (RdRP). The M segment encodes a protein of 83.4–96.7 kDa that is putatively a GP. Unlike the glycoprotein precursors of other phenuivirids, the fusavirus GP lacks homology to the conserved domains of phlebovirus glycoprotein G1 and phlebovirus glycoprotein G2 fusion. The S segment encodes a protein of 29.8–31.9 kDa that is homologous to tenuivirus/phlebovirus N domains, as well as a smaller protein of 16.6–16.9 kDa, the function of which remains unknown. (Navarro et al., 2018a, Navarro et al., 2018b, Chiapello et al., 2020).

Genome organization and replication

The fusavirus genome consists of two negative-sense RNAs and one ambisense RNA (Figure 1 Fusavirus). The fusavirus genome arrangement is similar to that of bandaviruses and uukuviruses (Figure 2 Phenuivridae). The L segment encodes the L protein that includes the RdRP domain. The M segment encode GP, which lacks the phlebovirus glycoprotein G1 and the phlebovirus glycoprotein G2 fusion domain as well as the C-terminal Ig-like domain. Its potential functional congruence with GPs of other phenuivirals remains to be elucidated. The S segment encodes two proteins, N and NSs, however, the NSs is missing in Fusarium asiaticum mycobunyavirus 1, whereas Sclerotinia sclerotiorum negative-stranded RNA virus 5 encodes additionally another NSs of unknown function. Since most mycoviruses encode a movement protein that enables cell-to-cell movement in fungus hosts and a viral suppression protein that counteracts fungus antiviral defence mechanisms based on RNA silencing, one or more of these proteins encoded by fusaviruses may possibly interfere with RNA silencing. Details of virus replication are unknown (Navarro et al., 2018a, Navarro et al., 2018b, Chiapello et al., 2020, Kormelink et al., 2021).

Figure 1 Fusavirus. Genome organization of some fusaviruses. Coloured boxes depict ORFs that encode L, large protein; GP, glycoprotein precursor; and N, nucleocapsid protein. A white box depicts an ORF that encodes MSs, a non-structural protein.

Biology

Host range

Fusaviruses have been detected by high-throughput sequencing of RNAs from the plant-pathogenic fungi Alternaria tenuissima ((Kunze) Wiltshire, 1933), Fusarium asiaticum O'Donnell, T. Aoki, Kistler & Geiser, 2004, and Sclerotinia sclerotiorum (Lib.) de Bary, 1884 (Navarro et al., 2018a, Navarro et al., 2018b).

Species demarcation criteria

The criteria demarcating species in the genus are:

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

Related, unclassified viruses

Virus names and virus abbreviations are not official ICTV designations.