Engineering Secondary Metabolism in Plants: Approaches, Successes and Opportunities

Andrew M. Hall-Ponselè Engineering secondary metabolism in plants: approaches, successes and opportunities

Engineering secondary metabolism in plants: approaches, successes and opportunities

Andrew M. Hall-Ponselè

Abstract Plant secondary metabolites include many medically, nutritionally and industrially important compounds that frequently accumulate at very low levels in nature. Attempts have been made to increase yields of secondary metabolites in plants with varying degrees of success. Metabolic engineering in plants is made difficult be pleiotropic effects, often the results of the depletion of carbon flux into competing branches of metabolism, caused by the incorrect assumption that precursor supply is effectively non-limiting. With increasing knowledge of metabolic flux control and genome-scale metabolic modelling, more informed metabolic engineering is now possible. This needs to take into account precursor availability, and the metabolic network as a whole, in addition to product sequestration and the accumulation of toxic intermediates. Introduction Verpoorte [1] defines secondary metabolites as “compounds with a restricted occurrence in taxonomic groups, that are not necessary for a cell (organism) to live, but play a role in the interaction of the cell (organism) with its environment, ensuring survival of the organism in its ecosystem.” Up to 200,000 distinct chemical species are estimated to exist in the plant kingdom [2], almost all of which are secondary metabolites. These are synthesised by a variety of pathways that branch from primary metabolism. Secondary metabolites include compounds that are essential for photosynthesis (e.g. the isoprenoid plastoquinone), defence (e.g. the quinolizidine alkaloids [3]) and attraction of seed dispersers (e.g. the anthocyanins [4]). They are also a major source of revenue for the pharmaceutical, food and cosmetics industries. Increasing yields of specific secondary metabolites in plants could result in...