Seeds as Bioreactors

The demand for recombinant therapeutic molecules has dramatically increased worldwide. Compared with conventional expression systems, several plant-based bioreactor systems are cost-effective partly due to the ease of agricultural scale-up. Among these systems, seeds as bioreactor platforms are especially attractive. In plant seeds, protein storage vacuoles (PSVs) and oil bodies (OBs) are two major storage compartments which are suitable for recombinant protein accumulation. Here we compare the present plant-based platforms including plant suspension cells, hairy root systems, chloroplast-expression, and seed systems. Further we introduce the detailed mechanisms of protein subcellular targeting to PSVs and OBs, as the basis for accumulating proteins in seed systems. Recombinant therapeutic proteins successfully produced using seed-based bioreactors have been summarized and selected cases are discussed in detail. Finally, we discuss the multiple factors including practical considerations for maximizing the yield and modifying recombinant proteins properly so that the recombinant versions closely resemble the native proteins.