Abstract
Plants are a promising expression system for the production of recombinant proteins. However, low protein productivity remains a major obstacle that limits extensive commercialization of whole plant and plant cell bioproduction platform. Plastid genetic engineering offers several advantages, including high levels of transgenic expression, transgenic containment via maternal inheritance, and multigene expression in a single transformation event. In recent years, the development of optimized expression strategies has given a huge boost to the exploitation of plastids in molecular farming. The driving forces behind the high expression level of plastid bioreactors include codon optimization, promoters and UTRs, genotypic modifications, endogenous enhancer and regulatory elements, posttranslational modification, and proteolysis. Exciting progress of the high expression level has been made with the plastid-based production of two particularly important classes of pharmaceuticals: vaccine antigens, therapeutic proteins, and antibiotics and enzymes. Approaches to overcome and solve the associated challenges of this culture system that include low transformation frequencies, the formation of inclusion bodies, and purification of recombinant proteins will also be discussed.
Highlights
The demand for recombinant proteins such as biopharmaceutical proteins and industrial enzymes is expected to rise dramatically in the near future
In a recent study, a hepatitis C virus core polypeptide expressed in chloroplasts, the results suggested that the codonoptimised gene increased monocistronic core mRNA levels by at least 2-fold and core polypeptides by over 5-fold, relative to the native viral gene [35]
The results showed that the highest levels of recombinant protein expression were obtained using either the atpA or psbD 5 UTRs, while the nature of the 3 -UTR invariably had little effect on reporter protein accumulation [51]
Summary
The demand for recombinant proteins such as biopharmaceutical proteins and industrial enzymes is expected to rise dramatically in the near future. The strong global demand for low-cost and high-yield recombinant proteins is the impetus driving molecular farming, in developing nations [2]. Commercial production of such recombinant proteins has traditionally relied on bacterial fermentation or mammalian cell-based production. Production of recombinant proteins in transgenic plants was initially based on integration of a target gene into the nuclear genome and later included transformation of the chloroplast genome [1]. We give main advantages on plastid information, factors for high-yield production, the expression level of recombinant proteins in plastid, the challenges directions in the development and commercialization of recombinant proteins in plastid expression system are discussed
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