Production of plant secondary metabolites: a historical perspective

Studies on plant secondary metabolites have been increasing over the last 50 years. These molecules are known to play a major role in the adaptation of plants to their environment, but also represent an important source of active pharmaceuticals. Plant cell culture technologies were introduced at the end of the 1960s as a possible tool for both studying and producing plant secondary metabolites. Different strategies, using in vitro systems, have been extensively studied with the objective of improving the production of secondary plant compounds. Undifferentiated cell cultures have been mainly studied, but a large interest has also been shown in hairy roots and other organ cultures. Specific processes have been designed to meet the requirements of plant cell and organ cultures in bioreactors. Despite all of these efforts of the last 30 years, plant biotechnologies have led to very few commercial successes for the production of valuable secondary compounds. Compared to other biotechnological fields such as microorganisms or mammalian cell cultures, this can be explained by a lack of basic knowledge about biosynthetic pathways, or insufficiently adapted reactor facilities. More recently, the emergence of recombinant DNA technology has opened a new field with the possibility of directly modifying the expression of genes related to biosyntheses. It is now possible to manipulate the pathways that lead to secondary plant compounds. Many research projects are now currently being carried out and should give a promising future for plant metabolic engineering.