''Caulimoviridae'' is a family of

viruses A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's ...

infecting plants. There are 94 species in this family, assigned to 11 genera. Viruses belonging to the family ''Caulimoviridae'' are termed double-stranded DNA (dsDNA) reverse-transcribing viruses (or pararetroviruses) 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 their lifecycle.

Taxonomy

The following genera are recognized: *'' Badnavirus'' *'' Caulimovirus'' *'' Cavemovirus'' *'' Dioscovirus'' *'' Petuvirus'' *'' Rosadnavirus'' *'' Ruflodivirus'' *'' Solendovirus'' *'' Soymovirus'' *'' Tungrovirus'' *'' Vaccinivirus''

Virus particle structure

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 (ORF), as observed in petuviruses, to eight ORFs such as in the soymoviruses. Proteins encoded by the viral genomes include

reverse transcriptase A reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template, a process termed reverse transcription. Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genom ...

-ribonuclease H,

aspartic protease Aspartic proteases are a catalytic type of protease enzymes that use an activated water molecule bound to one or more aspartate residues for catalysis of their peptide substrates. In general, they have two highly conserved aspartates in the activ ...

s, nucleocapsids and transactivators — there are other proteins essential for replication that have yet to be assigned a specific function. 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 (due to transcription occurring twice for some parts of the DNA). 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

. 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

retrovirus A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. Once inside the host cell's cytoplasm, the virus uses its own reverse transcriptas ...

es. 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 Retroviral integrase (IN) is an enzyme produced by a retrovirus (such as HIV) that integrates—forms covalent links between—its genetic information into that of the host cell it infects. Retroviral INs are not to be confused with phage in ...

. The presence of endogenous viral elements (EVEs) 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 (illegitimate recombination) during DNA repair mechanisms. Most plant EVEs are non infectious. However, infectious ''Caulimoviridae'' EVEs have been reported in the genome of petunia ('' Petunia vein clearing virus),'' banana (''Banana streak OL virus'', ''Banana streak GF virus'', ''Banana streak IM virus)'' and ''Nicotiana edwardsonii'' (''Tobacco vein clearing virus'').

References

External links

ICTV Report: ''Caulimoviridae''
* * * {{Taxonbar, from=Q264052 Viral plant pathogens and diseases Virus families Ortervirales