Notes on Genus: Benyvirus

rigid rods

Type member: Beet necrotic yellow vein virus

Contents

Members of this Genus
General Description
Morphology
Electron Micrograph
Genome
Genus Genomic Organization
Genome Map
Type Member Genomic Organization
All Known Sequences
Curated Sequences

General Description

Benyviruses (from beet necrotic yellow 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.

Morphology

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.

Genome

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 kDacoat protein readthrough, involved in fungus transmission
4 42 kDa4-6 = Triple gene block probably involved in cell-to-cell movement
5 13 kDa
6 15 kDa
7 14 kDaCysteine-rich protein with unknown function
RNA3 (c. 1775 nucleotides) produces:
8 25 kDaaffecting symptom expression
9 4.6 kDa
RNA4 (c. 1370 nucleotides) produces:
10 31 kDanecessary for efficient fungus transmission
RNA5 (c. 1350 nucleotides; not present in all isolates) produces:
11 26 kDaUnknown function