Notes on Genus: Tospovirus

enveloped spheres

Type member: Tomato spotted wilt virus

General Description

This is the only plant virus genus in the large family Bunyaviridae. Its name is derived from the type member, tomato spotted wilt virus.

Morphology

Virions pleomorphic in shape and size, spheroidal and enveloped, 80-110 nm in diameter. 3 filamentous nucleocapsids per envelope, each 200-3000 nm long (depending on arrangement) and 2-2.5 nm in diameter. Symmetry helical.

Virions composed of 1-2 % nucleic acid, over 50 % protein and 20-30 % lipid.

Genome

Linear, tripartite ssRNA: L (c.8900 nt), M (c.4800 nt) and S (c.2900 nt). Genomic nucleic acid is negative sense (RNA-L), or ambisense (RNA-M and RNA-S). Nucleotide sequences of 3'-termini are complementary to similar regions on the 5' end, thus forming a panhandle.

Genus Genomic Organization

Translation of the RNA is believed to produce a polymerase from RNA-L (complementary sense), while RNA-M and RNA-S each produces one product in the virus sense and one in the complementary sense. The coat protein is the complementary sense product of RNA-S.

Type Member Genomic Organization

Translation of the RNA is believed to produce the following products:

ORF	Segment	complementary	Size	Putative function
1	RNA-L	complementary	331.5 kDa	RNA polymerase
2	RNA-M	viral	33.6 kDa	NS_M possibly involved in cell-to-cell movement
3	RNA-M	complementary	127.4 kDa	precursor of glycoproteins G1 and G2
4	RNA-S	viral	52.4 kDa	NS_S, unknown function
5	RNA-S	complementary	28.8 kDa	N, nucleoprotein (Coat protein)