Metabolic engineering strategies for the optimization of medicinal and aromatic plants: realities and expectations

In recent years, strategies and techniques for the production of natural compounds (plant derived fine chemicals) and/or the breeding of medicinal and aromatic plants has expanded. Efficient production of high value natural products with medicinal and cosmetic purpose (e.g. essential oils, paclitaxel, artemisinin, and vincristine) is the main target. Metabolic engineering and pathway optimization with the aim to reduce costs and increase productivity are the main focus of academia and industry. Until now, only a limited number of plant cell cultures and isolated enzymes gave sufficiently high production for commercial purposes. Therefore research strategies have been shifted to metabolic engineering. Engineering of microorganisms has proven to be a valuable tool and the concept has been transferred to plant science opening new promising perspectives. Engineering has been conducted for crop plants, but the application of this technique to medicinal plants has not yet been explored well so far. Nowadays the cloning and expression of multiple genes and genomic integration are of high interest. This allows the reconstitution of biosynthetic pathways in heterologous organisms, being either plants or microorganisms. Combining basic science and applied engineering in this research area has been named combinatorial biosynthesis and later as synthetic biology. Synthetic biology comprises a large number of subareas, including enzymology, protein assembly and interactions, metabolomics, gene regulation, signal transduction and computational biology and is considered as an important future approach for biotechnological plant optimization. Synthetic biology has exciting perspectives for the exploitation of medicinal and aromatic plants, in order to increase the level of desired natural products, to gain insight in metabolic pathways even for new similar chemicals, to improve nutritional and health promoting effects of foods (nutraceuticals), and to reduce the amount of undesired side products with potential toxic or allergic activities.