Labdane diterpenes (LDs), and especially sclareol, are important feedstocks for the pharmaceutical and cosmetic industries, and therefore several lines of research have led to their heterologous production in non-photosynthetic microbes and higher plants. The potential of microalgae as bioreactors of natural products has been established for a variety of bioactive metabolites, including terpenes. In this work, a codon optimized sequence encoding a key plant labdane-type diterpene (LD) cyclase, copal-8-ol diphosphate synthase from Cistus creticus (CcCLS), was introduced into the chloroplast genome of Chlamydomonas reinhardtii. Of 49 transplastomic algal lines, 12 produced variable amounts of four LD compounds, namely ent-manoyl oxide, sclareol, labda-13-ene-8α,15-diol and ent-13-epi-manoyl oxide. The total LD concentrations measured in the transplastomic lines reached 1.172 ± 0.05 μg/mg cell DW for the highest overall producer, while the highest yield for sclareol was 0.038 ± 0.001 μg/mg cell DW. Thus, transplastomic expression of a key plant labdane diterpene cyclase in the C. reinhardtii chloroplast genome enabled the production of important plant-specific LD compounds. © 2019

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