''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. Viruses are found in almo ...

infecting plants. The family contains 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

Structure

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 In molecular biology, reading frames are defined as spans of DNA sequence between the start and stop codons. Usually, this is considered within a studied region of a prokaryotic DNA sequence, where only one of the six possible reading frames ...

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

reverse transcriptase A reverse transcriptase (RT) is an enzyme used to convert RNA genome to DNA, a process termed reverse transcription. Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genomes, by retrotransposon mobi ...

(RT), a ribonuclease H (RnaseH), aspartic proteases (AP), capsids (CP), 30K movement proteins (MP) and viral associated proteins (VAP) . Some ORF code for proteins of unknown function. The AP, RT and RnaseH are coded in the same ORF and produce a polyprotein. The RT protein unify the five family in the order ''Ortervirales'' : ''Belpaoviridae'', ''Caulimoviridae'', ''

Metaviridae ''Metaviridae'' is a family of viruses which exist as Ty3-gypsy LTR retrotransposons in a eukaryotic host's genome. They are closely related to retroviruses: members of the family ''Metaviridae'' share many genomic elements with retroviruses, i ...

'', '' Pseudoviridae'' and ''

Retroviridae 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. After invading a host cell's cytoplasm, the virus uses its own reverse transcriptase ...

'' ''.'' However, unlike the other four families, the ''Caulimoviridae'' genomes do not encode an integrase protein. Thus their integration is not mandatory in their replication life cycle .

Replication

The virion enter in the host cell and will reach the nucleus. The capsid protein are disassembled and the circular dsDNA enter the nucleus via the nuclear pore. The viral DNA forms supercoiled mini-chromosome structures upon entering the host nucleus, where it is transcribed by the host polymerase II into polyadenylated

RNA Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...

which is terminally redundant (due to transcription occurring twice for some parts of the DNA). Newly transcribed RNA are exported into 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.

Integration

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''
* * * {{Authority control Viral plant pathogens and diseases Virus families Ortervirales