Synthetic biology for production of natural and new-to-nature terpenoids in photosynthetic organisms.

With tens of thousands of characterized members, terpenoids constitute the largest class of natural compounds that are synthesized by all living organisms. Several terpenoids play primary roles in the maintenance of cell membrane fluidity, as pigments or as phytohormones, but most of them function as specialized metabolites that are involved in plant resistance to herbivores or plant-environment interactions. Terpenoids are an essential component of human nutrition, and many are economically important pharmaceuticals, aromatics and potential next-generation biofuels. Because of the often low abundance in their natural source, as well as the demand for novel terpenoid structures with new or improved bioactivities, terpenoid biosynthesis has become a prime target for metabolic engineering and synthetic biology projects. In this review we focus on the creation of new-to-nature or tailor-made plant-derived terpenoids in photosynthetic organisms, in particular by means of combinatorial biosynthesis and the activation of silent metabolism. We reflect on the characteristics of different potential photosynthetic host organisms and recent advances in synthetic biology and discuss their utility for the (heterologous) production of (novel) terpenoids.