Plant Viruses (Cauliflower Mosaic Viruses OR CaMV and Geminivirus)

Plant Viruses (Cauliflower Mosaic Viruses OR CaMV and Geminivirus) - Cauliflower mosaic virus (CaMV), tobacco mosaic virus (TMV) and geminiviruses are three groups of viruses that have been used as vectors for cloning of DNA segments. CaMV infects particularly the members or cruciferac and has a double stranded DNA molecule, 8 kbp in size, whose sequence is now known.

Following infection, the virus spreads systematically throughout the plant ill a very high copy number reaching upto 105 virus particles per cell. These features make CaMV a suitable vector for transformation of higher plants although there are instances of the use or other viruses also as vectors leading to the production of transgenic plants.

Geminiviruses comprise a group of single stranded DNA plant viruses causing important diseases in cassava, maize and other cereals. They replicate via double stranded DNA forms and have been subdivided into two groups, one infecting monocots and transmitted by leafhoppers and the other infecting dicots and transmitted by whitefly.

The dicot geminiviruses have two DNA segments in their genome, DNA A and DNA B, both essential for infection by mechanical inoculation. DNA A carries all genes responsible for replication.

It has been shown that deletions in coat protein gene do not destroy infectivity of the virus, which means that long deletions in this region can be used to insert foreign DNA to obtain gene constructs that will be extremely useful as amplification and expression vectors in plants.

Further, since the coat proteins are the most abundant proteins synthesized by the virus, promoters of coat protein genes can be used for high level expression of cloned genes. CL V and TGMV have already been tested for their ability to allow multiplication and expression of a cloned gene.