Notes on Genus: Waikavirus
Type member: Rice tungro spherical virus
This is one of the genera in the plant picornavirus family Secoviridae
and is also known as the rice tungro spherical virus group. The name comes from the Japanese word describing the symptoms of the type member, rice tungro spherical virus. Members of this genus are transmitted by leaf hoppers and transmission depends on a self-encoded helper protein, distinct from the coat protein. At least some are also able to act as helper viruses to enable the vector transmission of other plant viruses. Thus rice tungro spherical virus acts as a helper for rice tungro bacilliform virus (genus Badnavirus
) and anthriscus yellows virus acts as a helper for parsnip yellow fleck virus (genus Sequivirus
Virions isometric (icosahedral) about 30 nm in diameter with no obvious structural features.
Monopartite, single-stranded polyadenylated positive-sense RNA about 12000 nucleotides long. 3' terminus has a poly(A) tract. 5' terminus probably has a genome-linked protein (VPg).
Genus Genomic Organization
The sole (or major) translation product is a polyprotein, which is subsequently processed into a number of products of known or unknown function, including three coat proteins. There may also be two short open reading frames (ORFs) downstream of the polyprotein, but this has still to be confirmed.
Type Member Genomic Organization
This virus causes only mild or indistinct symptoms on its own but, when associated with rice tungro bacilliform badnavirus (RTBV), the serious rice tungro disease ensues. In the disease complex, RTSV acts as a "helper" enabling RTBV to be transmitted by the leafhopper. The sole (or major) translation product is a polyprotein, which is subsequently processed into a number of products of known or unknown functions:
|P1||c. 70 kDa|| ||Unknown function |
|CP1||22.9 kDa ||coat protein 1|
|CP2 ||22.3 kDa||coat protein 2|
|CP3||30 kDa|| ||coat protein 3|
|?|| ||region of unknown product(s)|
|Pro ||c. 36 kDa?||Cysteine protease |
|Pol||c. 70 kDa? ||Polymerase|
There may also be two short open reading frames (ORFs) downstream of the polyprotein, but this has still to be confirmed.