Progress towards commercialization of plastid transformation technology.

Tobacco chloroplasts are ready to be tested as a platform for the expression of recombinant proteins on a commercial scale. They hold the promise of reproducible yields of 5-25% of total soluble cellular protein in leaves and reliability has been achieved through refinement of an expression toolkit that includes vectors, recently developed expression cassettes and systems for marker gene removal. Implementation of plastid transformation technology in other crops, however, has met with difficulty and has delayed agronomic applications.