Notes on Genus: Fijivirus
icosahedra
Type member: Fiji disease virus
Contents
General Description
The genus
Fijivirus (named from the type member) is one of 3 plant virus genera in the family
Reoviridae. Members have 10 genome segments and are transmitted by planthoppers. They differ from
Oryzaviruses in the sizes of the genome segments and in having two types of surface projection on their (slightly larger) virions. The viruses infect only the phloem tissues of their
Gramineae hosts and replicate in both the plant and the vector. All members cause tumours in infected plants. Three subgroups have been recognised on their serological relationships.
Morphology
Virions isometric (icosahedral), 65-70 nm in diameter, not enveloped and with obvious apparently round, regular surface structure. There are two distinct types of surface projection: "A"-type spikes (restricted to 12 vertices of about 11 nm in length and breadth) and 12 "B"-type spikes, about 8 nm long and 12 nm in diameter. There are at least six structural proteins.
Genome
Linear, double stranded RNA in 10 segments. Each virion contains a single copy of the entire genome. Total genome 27000-30500 base pairs long. The 3' terminus has neither a poly(A) tract nor a tRNA-like structure. All RNA segments have highly conserved nucleotide sequences at the 3'- and 5'-termini.
Genus Genomic Organization
Most of the segments are monocistronic but in plant pathogenic members, two of the smaller segments encode two proteins. The functions of most of these proteins is still uncertain and is complicated by the fact that segments carrying the same number in different viruses are often not homologous. For example, the major outer structural protein is encoded on segment 10 of RBSDV and MRDV (and probably FDV) but on segment 8 of NLRV and OSDV. The largest segment (S1) encodes the RNA polymerase.
Type Member Genomic Organization
| ORF | Segment | Size (nt) | Protein(s) encoded |
| 1 | S1 | 4532 | 170.6 kDa polymerase |
| 2 | S2 | 3820 | 137.0 kDa (perhaps major core structural protein) |
| 3 | S3 | 3623 | 135.5 kDa B-spike protein |
| 4 | S4 | 3568 | 133.2 kDa |
| 5 | S5 | 3150 | 115.3 kDa |
| 6 | S6 | 2831 | 96.7 kDa myosin-like protein |
| 7, 8 | S7 | 2194 | 41.7 kDa, 36.7 kDa |
| 9 | S8 | 1959 | 68.9 kDa (perhaps NTP-binding protein) |
| 10, 11 | S9 | 1843 | 38.6 kDa structural protein, 23.8 kDa |
| 12 | S10 | 1819 | 62.9 kDa (probably major outer structural protein) |
