Genetic engineering of algal chloroplasts: Progress and prospects

The last few years has seen an ever-increasing interest in the exploitation of microalgae as recombinant platforms for the synthesis of novel bioproducts. These could be biofuel molecules, speciality enzymes, nutraceuticals, or therapeutic proteins, such as antibodies, hormones, and vaccines. This exploitation requires the development of new genetic engineering technologies for those fast-growing, robust species suited for intensive commercial cultivation in bioreactor systems. In particular, there is a need for routine methods for the genetic manipulation of the chloroplast genome, for two reasons: firstly, the chloroplast genetic system is well-suited to the targeted insertion into the genome and high-level expression of foreign genes; secondly, the organelle is the site of numerous biosynthetic pathways and therefore represents the obvious “chassis,” on which to bolt new metabolic pathways that divert the carbon fixed by photosynthesis into novel hydrocarbons, pigments, etc. Stable transformation of the algal chloroplast was first demonstrated in 1988, using the model chlorophyte, Chlamydomonas reinhardtii. Since that time, tremendous advances have been made in the development of sophisticated tools for engineering this particular species, and efforts to transfer this technology to other commercially attractive species are starting to bear fruit. In this article, we review the current field of algal chloroplast transgenics and consider the prospects for the future.