Chloroplast Bioreactors For Synthetic Biology

Chloroplast transformation has several unique advantages including high levels of expression and transgene containment via maternal inheritance of chloroplast genomes. The highest levels of expression in the published literature (up to 70% of leaf protein) for engineering agronomic traits or human therapeutic proteins or industrial products were indeed achieved using this concept. Vaccine antigens bioencapsulated in plant cells upon oral delivery conferred both mucosal and systemic immunity and protection against bacterial, viral and protozoan pathogen challenge (Trends in Plant Science 14: 669-679, 2009). Oral delivery of autoantigens was effective against complications of type 1diabetes and hemophilia, by developing tolerance (PNAS 107: 7101-7106, 2010). Oral delivery of proinsulin or exendin-4 expressed in plant cells regulated blood glucose levels similar to injections (Plant Biotech J. 9: 585-598, 2011, 2012 online). Oral delivery of myelin basic protein degraded a-beta plaques in brains with advanced Alzheimer’s disease. Therefore, chloroplasts are ideal low cost bioreactors to deliver different therapeutic proteins to combat infectious or inherited diseases by eliminating expensive purification, cold storage, cold transportation and sterile delivery by injections.

Biofuel production from is limited by expensive enzymes to release fermentable sugars from lignocellulosic biomass. Chloroplast-derived crude-extract enzyme cocktails yielded more glucose from pine wood or citrus peel than commercial cocktails produced via fermentation and 1000-fold less expensive (Plant Biotech J. 8: 332-350, 2010). One of these enzymes, B-glucosidase, released active hormones from their inactive conjugates stored within chloroplasts and doubled plant biomass (Plant Physiology 155: 222-235, 2011). Recent advances in this field will be presented.