Engineering the plant cell factory for secondary metabolite production

Plant secondary metabolism is very important for traits such as flower colo r, flavor of food, and resistance against pests and diseases. Moreover, it is the source of many fine chemicals such as drugs, dyes, flavors, and frag rances. It is thus of interest to be able to engineer the secondary metabol ite production of the plant cell factory, e.g. to produce more of a fine ch emical, to produce less of a toxic compound, or even to make new compounds, Engineering of plant secondary metabolism is feasible nowadays, but it req uires knowledge of the biosynthetic pathways involved. To increase secondar y metabolite production different strategies can be followed, such as overc oming rate limiting steps, reducing flux through competitive pathways, redu cing catabolism and overexpression of regulatory genes. For this purpose ge nes of plant origin can be overexpressed, but also microbial genes have bee n used successfully. Overexpression of plant genes in microorganisms is ano ther approach, which might be of interest for bioconversion of readily avai lable precursors into valuable fine chemicals. Several examples will be giv en to illustrate these various approaches. The constraints of metabolic eng ineering of the plant cell factory will also be discussed. Our limited know ledge of secondary metabolite pathways and the genes involved is one of the main bottlenecks.