Notes on Family: Geminiviridae
twinned icosahedra
Contents
General Description
This family is characterised by its twinned (geminate) icosahedral particles and a circular, single-stranded DNA genome in one or two components. The only other known plant viruses with ssDNA genomes have many more, smaller, segments and are placed in the family
Nanoviridae. Genera are distinguished by the number of genome segments, genome organization, the type of vector and the host plants infected.
Morphology
Virions twinned (geminate) icosahedral, non-enveloped, 38 nm long and 22 nm in diameter. 22 capsomeres per nucleocapsid.
Genomen
Mono-, or bi-partite, circular single-stranded DNA. Total genome 2500-3000 or 4800-5600 nucleotides. There are coding regions in both the virion (+) and complementary (-) sense strands. All members have a single coat protein of 28-34 kDa and a replication (Rep) protein of
c. 41 kDa, that initiates rolling-circle replication. In all members, there is a potential stem-loop structure in the intergenic region that includes a conserved nonanucleotide sequence (TAATATTAC; TAAGATTCC in some genera) where ssDNA synthesis is initiated.
Genera in the Family
- Becurtovirus: one genome segment coding for 5 proteins (three forward and two reverse with a spliced replication initiation protein); TAAGATTCC virion strand origin of replication; transmitted by leafhoppers to dicotyledonous plants
- Begomovirus (Geminivirus subgroup III): transmitted by whiteflies (Bemisia spp.) to dicotyledonous plants: one or two genome segments
- Curtovirus (Geminivirus subgroup II): one genome segment coding for 7 proteins (three forward and four reverse); transmitted by leafhoppers or treehoppers to dicotyledonous plants
- Eragrovirus: one genome segment coding for 4 proteins (two forward and two reverse with an unspliced replication initiation protein); TAAGATTCC virion strand origin of replication; infects monocotyledonous plants; vector unknown
- Mastrevirus (Geminivirus subgroup I): one genome segment coding for 4 proteins (two forward and two reverse with a spliced replication initiation protein); transmitted by leafhoppers, usually to monocotyledonous plants
- Topocuvirus: one genome segment coding for 6 proteins (two forward and four reverse); transmitted by treehoppers to dicotyledonous plants
- Turncurtovirus: one genome segment coding for 6 proteins (two forward and four reverse); distantly related to curtoviruses; infects dicotyledonous plants; vector unknown
