Caulimoviridae


Caulimoviridae is a family of viruses infecting plants. There are currently 85 species in this family, divided among 10 genera.
Viruses belonging to the family Caulimoviridae are termed double-stranded DNA reverse-transcribing viruses i.e. viruses that contain a reverse transcription stage in their replication cycle. This family contains all plant viruses with a dsDNA genome that have a reverse transcribing phase in its lifecycle.

Taxonomy

The following genera are recognized:
All viruses of this family are non-enveloped. Virus particles are either bacilliform or isometric. The type of nucleocapsid incorporated into the virus structure determines the size of the viral particles. Bacilliform particles are approximately 35–50 nm in diameter and up to 900 nm in length. Isometric particles are on average 45–50 nm in diameter and show icosahedral symmetry.

Genome structure and replication

The genomes of viruses from this family contain monopartite, non-covalently closed circular dsDNA of 7.2–9.3 kbp with discontinuities in both genome strands at specific places. These genomes contain one open reading frame, as observed in petuviruses, to eight ORFs such as in the soymoviruses. Proteins encoded by the viral genomes include reverse transcriptase-ribonuclease H, aspartic proteases, nucleocapsids and transactivators — there are other proteins essential for replication that have yet to be assigned a specific function.
GenusStructureSymmetryCapsidGenomic arrangementGenomic segmentation
RosadnavirusIcosahedralT=7Non-envelopedCircularMonopartite
CavemovirusIcosahedralT=7Non-envelopedCircularMonopartite
PetuvirusIcosahedralT=7Non-envelopedCircularMonopartite
CaulimovirusIcosahedralT=7Non-envelopedCircularMonopartite
SoymovirusIcosahedralT=7Non-envelopedCircularMonopartite
BadnavirusBacilliformT=3Non-envelopedCircularMonopartite
SolendovirusIcosahedralT=7Non-envelopedCircularMonopartite
TungrovirusBacilliformT=3Non-envelopedCircularMonopartite

Replication takes place in both the cytoplasm and the nucleus of host cells. Firstly, the viral genome enters the cytoplasm. The viral DNA forms supercoiled mini-chromosome structures upon entering the host nucleus, where it is transcribed into polyadenylated RNA which is terminally redundant. Newly transcribed RNA enters the cytoplasm where it is either translated into viral proteins, or retrotranscribed into new copies of the dsDNA viral genome by the viral reverse transcriptase. New dsDNA genomes are encapsidated in the cytoplasm and released.
The replication process involves a retro transcription step and an RNA intermediate, therefore viruses from the family Caulimoviridae are not considered true dsDNA viruses — instead they are termed DNA reverse-transcribing viruses. They share this characteristic with retroviruses. However, unlike retroviruses, viruses from the family Caulimoviridae do not require the integration of the viral genome into the genome of their hosts in order to replicate and for this reason their genome does not encode the enzymatic protein integrase.
The presence of endogenous viral elements in plant genomes is widespread. and most known plant EVEs originate from viruses with DNA genomes in the family Caulimoviridae. Integration is thought to occur through non-homologous end-joining during DNA repair mechanisms. Most plant EVEs are non infectious. However, infectious Caulimoviridae EVEs have been reported in the genome of petunia, banana and Nicotiana edwardsonii.
GenusHost detailsTissue tropismReplication siteAssembly siteTransmission
RosadnavirusPlants-NucleusCytoplasmAphids
CavemovirusPlants-NucleusCytoplasmAphids
PetuvirusPlants-NucleusCytoplasmGrafting, activation of infectious EVEs
CaulimovirusPlants-NucleusCytoplasmAphids
SoymovirusPlants-NucleusCytoplasmAphids
BadnavirusPlants-NucleusCytoplasmMealybugs, activation of infectious EVEs
SolendovirusPlants-NucleusCytoplasmActivation of infectious EVEs
TungrovirusPlants-NucleusCytoplasmAphids