Notes on Genus: Curtovirus
Type member: Beet curly top virus
This is one of 7 genera in the family Geminiviridae
. It is also known as Geminivirus Subgroup II or the beet cur
p virus group. It differs from the genus Begomovirus
in leafhopper or treehopper transmission and in having a monopartite genome. It differs from the other monopartite genera because the genome encodes 7 proteins and its members infect dicotyledonous plants. The genus Mastrevirus
has a slightly smaller genome, encoding 3 or 4 proteins and most members infect graminaceous plants, while the genus Topocuvirus
is characterised by a genome encoding 6 proteins.
Virions are geminate (twinned) icosahedra, not enveloped, 38 nm long and 22 nm in diameter. 22 capsomeres per nucleocapsid.
Monopartite, closed circular, single stranded DNA, 2900-3100 nucleotides long.
Genus Genomic Organization
In most members of the genus there are three open reading frames (ORFs) in the positive (virion) sense and four in the negative (complementary) sense:
|V1||+||29-30 kDa ||coat protein|
|V2||+||12-15 kDa||ss/dsDNA regulator|
|V3||+||10 kDa ||movement protein|
|C1||-||39-44 kDa ||replication protein|
|C2||-||16-20 kDa||unknown function|
|C3||-||16 kDa||similar to the replication enhancer protein of begomoviruses|
|C4||-||9-13 kDa||initiates cell division; symptom determinant|
The sequence of HrTV lacks C3 and one of the sequences of BSCTV has a fourth ORF in the positive sense.
Type Member Genomic Organization
Examination of the type member sequence (about 3000nt) in the light of those for other members of the genus suggests that there are three open reading frames (ORFs) in the positive (virion) sense and four in the negative (complementary) sense:
|V1||+||29.6 kDa ||coat protein|
|V2||+||13.1 kDa ||ss/ds DNA regulator|
|V3||+||10.0 kDa ||movement protein|
|C1||-||44.0 kDa ||replication protein|
|C2||-||20.0 kDa ||unknown function|
|C3||-||16.1 kDa ||putative replication enhancer protein |
|C4||-||9.7 kDa ||initiates cell division; symptom determinant|