Replication
CaMV replicates by reverse transcription. Initially all the gaps present in the genome are sealed and the covalently closed DNA then associates with host histones to form a super coiled mini chromosome. Transcription of this mini chromosome produces 35s RNA which translates protein as well as forming dsDNA by the process of reverse transcription. New viral particles are produced which are targeted to inclusion bodies & are released outside.
The Cauliflower Mosaic Virus promoter (CaMV 35S) is used in most transgenic crops to activate foreign genes which have been artificially inserted into the host plant. It is inserted into transgenic plants in a form which is different to that found when it is present in its natural brassica plant hosts. This enables it to operate in a wide range of host-organism environments which would otherwise not be possible.
CaMV contains about 8 kb double-strand DNA genome and produces spherical particles. CaMV infections are systemic, and even its DNA is infectious when inoculated on abraded plant surfaces. The CaMV genome has 8 tightly packed genes, of which only two small genes, genes II and VII, are nonessential; as a result, only these two genes can be replaced/deleted without a loss of infectivity. In addition, modified CaMV genomes exceeding the natural genome size (8024 bp) by even a few hundred bp are not packaged into virions. These two factors seriously limit the size of DNA insert clonable in CaMV. Bacterial dhfr (dihydrofolate reductase) gene was inserted in the CaMV genome in place of gene II, and was successfully expressed in plants. Cauliflower mosaic virus (CaMV) is the type member of the caulimoviruses, one of the six genera in the Caulimoviridae family, pararetroviruses that infect plants (Pringle, 1999). Pararetroviruses replicate through reverse transcription just like retroviruses, but the viral particles contain DNA instead of RNA (Rothnie et al., 1994). Structure
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