Notes on Genus: Oryzavirus
Type member: Rice ragged stunt virus
This is one of 3 plant virus genera in the family Reoviridae
. Members have 10 genome segments and are transmitted by planthoppers. They differ from Fijiviruses
in the sizes of the genome segments and in having only one type of surface projection on their (slightly smaller) 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. The name derives from the scientific name (Oryza sativa
) of rice, the host of the type member, rice ragged stunt virus.
Virions isometric (icosahedral), 57-65 nm in diameter, not enveloped and with obvious apparently round, regular surface structure. There are distinct surface projections, "B"-type spikes, restricted to 12 vertices. These are about 8-10 nm in length and 23-26 nm wide at the base narrowing to 14-17 nm at the top.
Linear, double stranded RNA in 10 segments. Each virion contains a single copy of the entire genome. Total genome c.
27000 nucleotides long (c.
3900, 3800, 3700, 3800, 2700, 2200, 1950, 1900, 1130, 1160). 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 (5' GAUAAA.....GUGC 3').
Genus Genomic Organization
Each segment has one or at most two ORFs. The major coat protein is on segment 8 and the RNA-dependent RNA polymerase is on segment 4.
Type Member Genomic Organization
- Segment 1 (3849nt) encodes a core protein, possibly the B-spike protein, of 138 kDa
- Segment 2 (3808nt) encodes an inner core protein of 133 kDa
- Segment 3 (3699nt) encodes the major core capsid protein of 131 kDa
- Segment 4: (3823nt) encodes the RNA-dependent RNA polymerase of 141 kDa and (in a different, nested, reading frame) a protein of 37 kDa of unknown function
- Segment 5 (2682 nt) encodes a protein of 91 kDa with guanyltransferase (capping) activity
- Segment 6 (2157 nt) encodes a protein of 66 kDa
- Segment 7 (1938 nt) encodes a non-structural protein of about 68 kDa
- Segment 8 (1914 nt) encodes a protein of about 67 kDa, which is autocatalytically cleaved into a protease and the major coat protein
- Segment 9 (1132 nt) encodes the 38 kDa spike protein required for vector transmission
- Segment 10 (1162 nt) encodes a non-structural protein of about 32 kDa