Notes on Genus: Benyvirus
Type member: Beet necrotic yellow vein virus
Benyviruses (from be
ellow vein virus) had originally been classified with furoviruses
but have four or five genome segments, the RNA is polyadenylated and there is a triple gene block on RNA2. The vectors are Polymyxa
spp., root-infecting parasites, classified in the Plasmodiophorales
Virions rod-shaped, not enveloped. Usually straight with a distinct central canal. Generally of two or more modal lengths, up to c.
390 nm in length, (but difficult to estimate because they are fragile) and about 20 nm in diameter. Symmetry helical. Surface capsomere arrangement obvious. Pitch of helix 2.6 nm.
Linear, single-stranded, positive sense RNA in four or five segments. The 3'-terminus of each RNA has a polyA tract.
Genus Genomic Organization
There is a single ORF (polmerase) on RNA1,while the coat protein, followed by a readthrough domain is at the 5'-end of RNA2 followed by four other ORFs ncluding the triple gene block. RNA3 has one or two ORFs and there are one each on RNA4 and RNA5 (which is not present in all isolates or viruses). The smaller RNAs (3-5) of BNYVV can be lost during laboratory (mechanical) transmission. The function of the genes on these RNAs is not known for certain but RNA3 affects symptom production and RNA4 is necessary for efficient fungus transmission.
Type Member Genomic Organization
|RNA1 (c. 6750 nucleotides) produces:|
|1 ||237 kDa ||Polymerase |
|RNA2 (c. 4600 nucleotides) produces:|
|2 ||21 kDa ||coat protein|
|3 ||75 kDa||coat protein readthrough, involved in fungus transmission|
|4 || 42 kDa||4-6 = Triple gene block probably involved in cell-to-cell movement|
|5 ||13 kDa|
|6 ||15 kDa|
|7 ||14 kDa||Cysteine-rich protein with unknown function|
|RNA3 (c. 1775 nucleotides) produces:|
|8 || 25 kDa||affecting symptom expression|
|9 ||4.6 kDa|
| RNA4 (c. 1370 nucleotides) produces:|
|10 ||31 kDa||necessary for efficient fungus transmission |
|RNA5 (c. 1350 nucleotides; not present in all isolates) produces:|
|11 ||26 kDa||Unknown function |