The effect of the unfolded protein response on the production of recombinant proteins in plants

Recombinant proteins are currently produced through a wide variety of host systems, including yeast, E. coli, insect and mammalian cells. One of the most recent systems developed uses plant cells. While considerable advances have been made in the yields and fidelity of plant-made recombinant proteins, many of these gains have arisen from the development of recombinant factors. This includes elements such as highly effective promoters and untranslated regions, deconstructed viral vectors, silencing inhibitors, and improved DNA delivery techniques. However, unlike other host systems, much of the work on recombinant protein production in plants uses wild-type hosts that have not been modified to facilitate recombinant protein expression. As such, there are still endogenous mechanisms functioning to maintain the health of the cell. The result is that these pathways, such as the unfolded protein response, can actively work to reduce recombinant protein production to maintain the integrity of the cell. This review examines how issues arising from the unfolded protein response have been addressed in other systems, and how these methods may be transferable to plant systems. We further identify several areas of host plant biology that present attractive targets for modification to facilitate recombinant protein production.