Family: Phenuiviridae

Genus: Laulavirus

Distinguishing features

Seven viruses are assigned to the genus Laulavirus. Laulaviruses genomes comprise three negative-sense RNA segments encoding a large protein (L), a nucleocapsid protein (N) and a non-structural protein that likely functions as a movement protein (MP) that enables cell-to-cell movement in plant hosts. Based on well-supported Maximum Likelihood or Maximum Clade Credibility trees inferred from complete L protein sequences, viruses classified in the genus Laulavirus form a monophyletic cluster clearly distinguished from other phenuivirids (Tokarz et al., 2018, Bertazzon et al., 2020, Chiapello et al., 2020).

Virion

Virion morphology is unknown.

Nucleic acid

Laulavirus genomes encompass three segments of negative-sense RNA, designated RNA1 (7.1–7.4 kb), RNA2 (1.7–2.5 kb) and RNA3 (1.0–1.7 kb). The terminal nucleotides of each segment occur in a canonical, conserved sequence (in coding sense) 5′-ACACAAAGUC…GUCUUUGUGU-3′ and may form the panhandle structures typical of other members of the class Bunyaviricetes. All three segments 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. RNA1 encodes a protein with a predicted molecular mass of 256.2–274.9 kDa that includes a region homologous with the bunyaviral RNA-directed RNA polymerase (RdRP) domain. RNA2 encodes a protein of 46.0–79.1 kDa that shares sequence homology and/or structural characteristics with the MP of plant viruses. RNA3 encodes a protein of 28.0–29.7 kDa that is homologous with the tenuivirus/phlebovirus N domain (Tokarz et al., 2018, Bertazzon et al., 2020, Chiapello et al., 2020).

Genome organization and replication

The laulavirus genome consists of three negative-sense RNAs (Figure 1 Laulavirus). The laulavirus genome arrangement is similar to that of bociviruses and rubodviruses (Figure 2 Phenuivridae). The three segments putatively encode L, MP and N, respectively. The laulavirus RNA3 segment does not encode a non-structural protein, but RNA3 of grapevine associated cogu-like virus 4 exhibits an ambisense coding strategy and encodes a small non-structural protein of unknown function. Details of virus replication are unknown (Bertazzon et al., 2020, Chiapello et al., 2020, Rodriguez Coy et al., 2022).

Figure 1 Laulavirus. Genome organization of some laulaviruses. Coloured boxes depict ORFs that encode N, nucleocapsid protein and L, large protein. White boxes depict ORFs that encodes MP, non-structural cell-to-cell movement protein and NSv3, non-structural protein.

Biology

Laulavirus RNAs have been found by high-throughput sequencing of RNAs from apple valsa canker-associated fungi (Cytospora mali Grove, 1935), downy mildews [Plasmopara viticola (Berk. & M.A. Curtis) Berl. & De Toni, 1888)], entomopathogenic fungi [Cordyceps javanica (Frieder. & Bally) Kepler, B. Shrestha & Spatafora, 2017 in Kepler RM et al. (2017)], and esca-associated fungi obtained from apples and grapevines in China, Italy and Spain. Laulavirus RNAs have been also found from the RNA of switchgrasses (Panicum virgatum L., 1753) and black-legged ticks [Ixodes scapularis (Say, 1821)] in USA (Tokarz et al., 2018, Bertazzon et al., 2020, Chiapello et al., 2020).

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.