Body-Building Chloroplasts

Research paper p. 333--338

Body-building chloroplasts

Scientists have succeeded in turning choloroplasts -- the tiny granules in plant cells that generate energy from sunlight-into miniature factories for manufacturing therapeutic proteins. By inserting the gene encoding human somatotropin (hST) into the DNA of chloroplasts in tobacco plants, they have expressed soluble, active therapeutic protein at levels 300-fold higher than those previously attained using conventional transgenic plants containing genetically modified nuclear DNA. As chloroplast DNA is not transferred to pollen, the new type of transgenic plants may represent a more effective approach for containing foreign genes in the environment.

Until now, most genetic engineering has focused on introducing foreign genes into nuclear DNA, not the small amount of DNA that is located outside the nucleus in chloroplasts. In the present work, Jeffrey Staub and his colleagues show for the first time that hST-a fully active human secretory protein-can be expressed at high levels in tobacco when chloroplast DNA is engineered to carry the human gene. Using an antibiotic marker to track the foreign gene, they also show that crosses between these genetically modified plants and wild-type tobacco result in offspring that contain no inserted genes within their nuclear or chloroplast DNA. What's more, the authors could detect no foreign genes within the pollen of transgenic plants.

The ability to produce high levels of hST in tobacco plants with engineered chloroplasts has the potential to significantly reduce the cost of manufacturing the therapeutic, reduces the risk of foreign gene transfer to weedy relatives in the environment, and avoids the risk of viral contamination that can occur when recombinant protein is produced in mammalian cell culture.

Contact
(Author)
Dr. Jeffrey M. Staub
Monstanto Company
700 Chesterfield Parkway North, BB3G
St Louis, MO 63198
314 737 6645
Fax: 314 737 5223
[email protected]

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