1. Cauliflower Mosaic Virus

2. Plant Viruses:
Plant viruses are considered as efficient gene transfer agents as they infect the intact plants and amplify the transferred genes through viral genome replication
They are non integrative vectors Eg, Pepper mint mottle virus, Leaf curl virus

3. Criteria needed:
The virus must be capable of spreading from cell to cell through plasmodesmata
The viral genome should be able to replicate in the absence of viral coat protein and spreads from cell to cell
Elicit little or no disease symptoms
Should have broad range of host

4. CaulimoViruses
Caulimoviruses contain circular ds DNA and are spherical in shape
This group includes 15 viruses of which CaMV is the most important for gene transfer
The other caulimoviruses includes carnation etched virus, dahlia mosaic virus mirabilis mosaic virus and strawberry vein banding virus

6. Cauliflower Mosaic Virus
CaMV is a plant virus that infects mostly brassicaceae family( cauliflower and turnips) and Solanaceae species
CaMV is transmitted in a non circulatory manner by aphid species Mysus
It is a icosahedron structure with a diameter of 52nm built from 420 cap protein subu
nits

7. Genome of CaMV
Movement Protein, Insect transmission Factor, Structural Protein, Translational factor, Reverse Transcription, Cap

8. Thepromoter of the 35S RNA is a very strong constitutive promoter responsible for the transcription of the whole CaMV genome.
It is well known for its use in plant transformation.
It causes high levels of gene expression in dicot plants
The 35S RNA is particularly complex, containing a highly structured 600 nucleotide long leader sequence with six to eight short open reading frames
This leader is followed by seven tightly arranged, longer ORFs that encode all the viral proteins. The mechanism of expression of these proteins is unique, in that the ORF VI protein (encoded by the 19S RNA) controls translation reinitiation of major open reading frames on the polycistronic 35S RNA, a process that normally only happens on bacterial mRNAs

9. Use of CaMV in gene transfer
For effective transmission of CaMV the foreign DNA must be encapsulated in viral protein and the inserted gene should not interfere with native assembly of virus
CaMV does not contain any non coding region wherein foreign DNA can be inserted
But there a are two genes namely gene II and gene VII have
no essential functions for the virus
So the gene of interest can be replaced in the place of these two genes
Attractive feature is infection is systemic and the genome has 3 discontinuities

10.  Use of CaMV as a vector pertains to the bacterial dhfr (dihydroxy folatereductase) gene inserted in the place of gene II and successfully expressed in plants
This dhfr gene is needed for providing resistance to methotrexate( inhibitor of dhfr and extremely toxic to plants)
Limitation of CaMV:
Limited capacity for insertion
Infective capacity is lost if few hundreds of nucleotides are introduced
Because of its exceeding natural genome size they are not effectively suitable for gene transfer