Plastid transformation and its application in metabolic engineering

•A new selectable marker and an improved inducible expression system for plastids.•Plastid engineering provides access to a large repertoire of metabolic pathways.•Combination of plastome and genome engineering for optimized metabolite production.•Electrons can be directly transferred from ferredoxin to cytochrome P450 enzymes.•Feasibility of plastid engineering in edible crops opens up new applications.

Metabolic pathway engineering by transgene expression from the plastid (chloroplast) genome offers significant attractions, including straightforward multigene engineering by pathway expression from operons, high transgene expression levels, and increased transgene containment due to maternal inheritance of plastids in most crops. In addition, it provides direct access to the large and diverse metabolite pools in chloroplasts and non-green plastid types. Here, we review recent progress with extending the toolbox for plastid engineering and highlight selected applications in the area of metabolic engineering, including the combined engineering of nuclear and plastid genomes for the production of artemisinic acid, the direct harness of chloroplast reducing power for the synthesis of dhurrin and the use of an edible host for the production of astaxanthin.

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