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Molecular Farming in Brassica Crops

Dr. Maurice M. Moloney

Professor and Chair of Plant Biotechnology, University of Calgary
2500 University Drive N.W. Calgary, Alberta T2N 1N4 Canada
Email: Tel: (403)220-6823 Fax: (403)220-0704

Since the development of the fundamental techniques for plant genetic engineering, Brassica species particularly Brassica napus has been a focal point of much of the research conducted. It was therefore no surprise that in the commercialization of genetically-modified crops Brassica species figures among the first. The original genetic modifications to reach commercialization are based primarily on improving agronomic performance or ease of cultivation. These introductions have been very successful in North America, although the issue of exaggerated concerns about genetically modified crops in the food chain have limited their use so far in Europe and to some extent in the southern hemisphere. Nevertheless, the technology that has given rise to herbicide and insect resistant crops is now well established and once it is better understood by the consumer, it will probably be generally accepted worldwide. There is a vast array of potential targets for the improvement of agronomic properties, stress resistance and plant health, but the investment to develop these will only be justified if the first crops introduced can be traded like the basic commodities that they are.

Almost since the development of gene transfer technology, there has been an interest in expressing genes in plants, not for agronomic improvements, but rather to use plants as hosts (or "factories") for the production of high value products not normally produced in plants. Plants, and particularly plant seeds, have the potential to act as repositories for a wide range of proteins useful as therapeutics, industrial and food enzymes, or in structural or personal care applications.

The keys to developing these applications include regulation and optimization of gene expression in the seed and the creation of scaleable extraction and purification schemes.

Oilseeds, and particularly rapeseed, have been a model for developing such applications and have inspired a fundamental method for protein production and purification from seeds. This method is referred to as "oleosin technology".

Oleosin technology uses the unique properties of the highly lipophilic oleosin protein family. Oleosins target specifically to developing oil bodies or oleosomes present in all oilseeds. In rapeseed oleosins comprise about 10% of total seed protein. When recombinant proteins are combined with oleosins through the expression of gene fusions in transgenic oilseeds, the recombinant protein associates exclusively with oil bodies. This permits the recovery of the desired protein from seed extract using simple oil-water partitioning. This partitioning can be used as the basis of an efficient purification scheme. In this paper (and in the attached powerpoint file), the uses of oleosin technology as a means of expressing and recovering recombinant proteins from Brassica oilseeds will be described and critically discussed.

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