Plastid Proteostasis and Heterologous Protein Accumulation in Transplastomic Plants

Abstract

In spite of a huge number of reports on successful foreign protein production in plastid, in many cases the expression level of other recombinant proteins in the transplastomic plants appears to be very low or even undetectable. We believe that this is mainly due to our limited knowledge of the mechanisms in plastids influencing the maintenance of protein homeostasis, or proteostasis. Plastids retain a whole series of mechanisms for the preservation of their protein balance, including specific proteases, transcriptional and translational control, as well as molecular chaperones and enzymes useful in protein folding. Therefore, it is important to develop basic studies in factors regulating protein synthesis, stability, folding, targeting, and accumulation in plastids, including the protein quality control which contributes to the functional integrity of proteins. Our intention here is not to provide a comprehensive review of the mechanisms that regulate plastid proteostasis, but to discuss some recent insights into this field which might bring beneficial applications in plastid biotechnology for transgene expression and foreign protein accumulation.