Trafficking and Stability of Heterologous Proteins in Transgenic Plants

The ability to introduce foreign genes into plant species by techniques such as Agrobacterium -mediated transformation or by direct gene transfer (e.g., biolistics) has opened up the possibility of using transgenic plants as host organisms for the production of heterologous proteins (see ref. 1 for an excellent review). Although a number of host organisms (such as Escherichia coli , yeasts, and mammalian cell cultures) are already used for the production of recombinant proteins, plants have several advantages that make them highly attractive for this purpose. For example, the large-scale production and processing of plant material is a routine, cost-effective process carried out by every nation with any form of agricultural industry, thus reducing the need for specialized growth and harvesting equipment. Plants offer additional advantages as potential producers of recombinant proteins. Not only do they modify proteins (in terms of glycosylation, prenylation, and so on) in the same way as other higher eukaryotes (2 ), but also, since they transmit the transgene encoding the heterologous protein in a Mendelian fashion, the seed of a transgenic plant can be used as the source of further producing lines. This seed also serves as a convenient way of storing biologically viable transgenic material without the need for either cryopreservation or continual passaging/subculturing. The potential offered by transgenic plants has been widely appreciated and anticipated, and a range of innovative strategies have been taken to either alter the endogenous compositions of plant products, or use plants as bio-reactors for the synthesis and accumulation of heterologous proteins.