Genus: Betachrysovirus


Genus: Betachrysovirus

Distinguishing features

Members of the genus Betachrysovirus infect ascomycetous or basidiomycetous fungi.

Virion

Nucleic acid

Betachrysoviruses have four, five and in one case seven (Zhai et al., 2018) dsRNA genome segments ranging from 0.8 to 3.7 kbp, as exemplified by Botryosphaeria dothidea chrysovirus 1 (BdCV1) (Figure 2.Chrysoviridae), with segments of 2.9–3.7 kbp (Table 1.Betachrysovirus). The genome comprises 10.9–16.0 kbp in total. The dsRNA segments are individually encapsidated in separate particles.

Proteins

Virion proteins include the RNA-directed RNA polymerase (RdRP; P1), and the virus capsid protein (CP, often P2 but in some case P3 or P4).  The capsids of the cinquechrysoviruses (those with five dsRNA segments) appear to contain more than one type of structural protein.

Genome organization and replication

Although the RNA-directed RNA polymerase (RdRP) encoded by betachrysoviruses has the P7/ P-loop NTPase domain at the N-terminus as well as the RdRP conserved motifs, the other virally encoded proteins lack the motifs identified in alphachrysoviruses (e.g. motifs of predicted cysteine proteases). Furthermore, the capsids of the cinquechrysoviruses (those with five dsRNA segments) appear to contain more than one structural protein. The functions of betachryso-P3 and betachryso-P4 are unknown and there is no similarity between the betachryso-P3 and the N-terminus of the RdRP. The proteins encoded by dsRNA5 are non-homologous between members of different species and their function is also unknown. It is noteworthy that dsRNA5 is dispensable for replication of Magnaporthe oryzae chrysovirus 1-B as stable derivatives with 4 dsRNA segments can be readily obtained via sub-culturing (Urayama et al., 2014).

Table 1.Betachrysovirus. Genome content and encoded proteins of Botryosphaeria dothidea chrysovirus 1 (BdCV1)

Segment

bpa

Mass of encoded protein in Dab

Designation and function of encoded protein

dsRNA1

3,654

125,761 (1,116 aa)

P1, RdRP

dsRNA2

2,773

79,512 (748 aa)

P2, CP

dsRNA3

2,597

82,112 (746 aa)

Betachryso-P3, unknown

dsRNA4

2,574

77,141 (717 aa)

Betachryso-P4, unknown

a Deduced from sequence of full-length cDNA clones
b Predicted from aa sequence encoded by full-length cDNA; the numbers of aa residues is given in parentheses.

Species demarcation criteria

Species demarcation criteria:

  • Host of isolation
  • Nucleotide and deduced amino acid sequence data (≤ 70% and ≤ 53% aa sequence identity in the RdRP and CP, respectively)
  • length of dsRNA genome segments
  • length of 5′-UTR

Species demarcation considers a combination of each of the criteria listed above. While nucleotide and amino acid sequence relatedness are important criteria for species demarcation, the other listed criteria may be useful in demarcation of genetically closely related viruses that nevertheless belong to different species.

Member species

Exemplar isolate of the species
SpeciesVirus nameIsolateAccession numberRefSeq numberAvailable sequenceVirus Abbrev.
Alternaria alternata chrysovirusAlternaria alternata chrysovirus 1Japanese pear pathotype N18dsRNA1: LC350277; dsRNA2: LC350278; dsRNA3: LC350279; dsRNA4: LC350280; dsRNA5: LC350281dsRNA1: NC_040738; dsRNA2: NC_040739; dsRNA3: NC_040736; dsRNA4: NC_040740; dsRNA5: NC_040737Complete genomeAaCV1
Botryosphaeria dothidea chrysovirusBotryosphaeria dothidea chrysovirus 1LW-1dsRNA1: KF688736; dsRNA2: KF688737; dsRNA3: KF688738; dsRNA4: KF688739Complete genomeBdCV1
Colletotrichum fructicola chrysovirus 1Colletotrichum fructicola chrysovirus 1FJ-4dsRNA1: MG425969; dsRNA2: MG425970; dsRNA3: MG425971; dsRNA4: MG425972; dsRNA5: MG425973; dsRNA6: MG425974; dsRNA7: MG425975dsRNA1: NC_040485; dsRNA2: NC_040491; dsRNA3: NC_040487; dsRNA4: NC_040488; dsRNA5: NC_040486; dsRNA6: NC_040489; dsRNA7: NC_040490Complete genomeCfCV1
Fusarium graminearum chrysovirusFusarium graminearum dsRNA mycovirus 298-8-60dsRNA1: HQ343295; dsRNA2: HQ343296; dsRNA3: HQ343297; dsRNA4: HQ343298; dsRNA5: HQ343299Complete genomeFgV2
Fusarium graminearum chrysovirusFusarium graminearum mycovirus China 9China 9dsRNA1: HQ228213; dsRNA2: HQ228214; dsRNA3: HQ228215; dsRNA4: HQ228216; dsRNA5: HQ228217Complete genomeFgV-China 9
Fusarium oxysporum chrysovirus 2Fusarium oxysporum f. sp. dianthi mycovirus 1Fod116dsRNA1: KP876629; dsRNA2: KP876630; dsRNA3: KP876631; dsRNA4: KP876632dsRNA1: NC_027563; dsRNA2: NC_027564; dsRNA3: NC_027565; dsRNA4: NC_027566Complete genomeFodV
Magnaporthe oryzae chrysovirusMagnaporthe oryzae chrysovirus 1-AViet NamdsRNA1: AB560761; dsRNA2: AB560762; dsRNA3: AB560763; dsRNA4: AB560764; dsRNA5: AB700631dsRNA1: NC_014462; dsRNA2: NC_014465; dsRNA3: NC_014463; dsRNA4: NC_014464; dsRNA5: NC_038011Complete genomeMoCV1-A
Magnaporthe oryzae chrysovirusMagnaporthe oryzae chrysovirus 1-BViet NamdsRNA1: AB824667; dsRNA2: AB824668; dsRNA3: AB824669; dsRNA4: AB824670; dsRNA5: AB824671Complete genomeMoCV1-B
Penicillium janczewskii chrysovirus 1Penicillium janczewskii chrysovirus 1MUT4358dsRNA1: KT601115; dsRNA2: KT601116; dsRNA3: KT601117; dsRNA4: KT601118dsRNA1: NC_028495; dsRNA2: NC_ 028500; dsRNA3: NC_028496; dsRNA4: NC_028497Complete genomePjCV1
Penicillium janczewskii chrysovirus 2Penicillium janczewskii chrysovirus 2MUT4359dsRNA1: KT950836; dsRNA2: KT950837; dsRNA3: KT950838; dsRNA4: KT950839dsRNA1: NC_043672; dsRNA2: NC_043669 ; dsRNA3: NC_043670; dsRNA4: NC_043671Complete genomePjCV2

Virus names, the choice of exemplar isolates, and virus abbreviations, are not official ICTV designations.