Viral vectors plants

Compared with whole plants, there has been limited development of foreign protein expression systems specifically for use in tissue culture. Some modifications of expression constructs have resulted in improved protein accumulation or have allowed simplified protein recovery. However, in general, modified expression systems have been tested only in a restricted number of cases and have not resulted in the large increases in product yield required for plant cultures to compete with other foreign protein production vehicles. Transient expression techniques, for example using viral vectors, that have been developed for use in whole plants have not yet been applied in plant tissue culture. 

Further improvements to vims expression systems include trans-complementation of some of the virus functions from transgenic host plants (P12 plants for AlMV). By integrating parts of the viral vector into the plant chromosome, this system has the potential for multiple technical solutions that could overcome limitations of classical viral vectors [33]. Viral vectors can be used as molecular switches for tightly controlled, high-level transgene expression (Hull et al. unpublished data). 

Two types of PVX-based viral vectors have been generated for full-length protein production one of these involves the duplication of the CP subgenomic promoter in a manner analogous to the TMV-30B system mentioned earlier (Chapman et al., 1992). Inserts as large as GFP can be fused to the N-terminus of the PVX CP and expressed effectively in infected plant cells. Examples of protein expressed using this PVX-duplicated subgenomic promoter-based system include the E7 of human papillomavirus type 16,... 

Several plant viral vectors have been used to successfully produce vaccines and therapeutic proteins in plants. TMV-based expression vectors represent one of the more successful examples and have produced a wide array of therapeutic proteins such as a-trichosanthin, tumor-specific single-chain antibodies, and a number of vaccine antigens (Table 4.1) (Dalsgaard et al., 1997). More recent examples of plant viral expression vectors utilized for vaccine production are provided in detail in Koprowski and Yusibov (2001), Pogue et al. (2002), and Canizares et al. (2005). 

Canizares, M.C., Nicholson, L., and Lomonossoff, G.R (2005). Use of viral vectors for vaccine prodnction in plants. Immunol. Cell Biol. 83 263-270. 

Kumangai, M.H., Turpen, T.H., Weinzenttl, N., della-Cioppa, G., Turpen, A.M., and Donson, J. (1993). Rapid, high-level expression of biologically active alpha-trichosanthin in transfected plants by an RNA viral vector. Proc. Natl. Acad. Sci. U.S.A. 90 427-430. 

Yusibov, V., Shivprasad, S., Turpen, T.H., Dawson, W., and Koprowski, H. (1999). Plant viral vectors based on tobacco mosaic viruses. Curr. Top. Microbiol. Immunol. 240 81-94. 

A number of different methods for stable or transient genetic transformation of plants or plant cells have been developed [13-15]. These comprise particle bombardment, Agro actermm-mediated transformation, floral dip transformation, agrodrench, viral vectors, protoplast transformation and ultrasound. These are the main techniques for the genetic transformation of plants, and many of them have also been applied for the transformation of secondary metabolite pathways in an attempt to alter the metabolic pathways of target... 

The employment of viral vectors has also been practiced to genetically transform plants. Different plant viruses have been utilised for the insertion of genes into a variety of plant species. It is known that the... 

Table 4 Transient expression of heterologous genes in plant tissues using Agrobacterium-delivered T-DNA (no viral vector)...

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