Production of Aromatic Amino Acid Derivatives through Metabolic Engineering of Crop Plants

Summary

A large number of plant products of commercial value including essential amino acids, alkaloids, phenols and structural compounds are derived from the shikimate pathway, but it is poorly understood what control architectures are required to produce these compounds. The creation of transgenic plants with artificial metabolic sinks that produce shikimate derived end-products or which effectively down-regulate the production of others has been successfully used in our laboratory to eliminate tryptophan-derived indoleglucosinolates inBrassica napus(canola). The elimination of indoleglucosinolates in canola seeds would be useful since this could increase the palatability of canola protein meals which are used for feeding swine and poultry. We have also shown that important effects on aromatic amino acid levels are observed when artificial metabolic sinks for tryptophan are introduced into transgenic plants. Transgenic potatoes which express tryptophan decarboxylase accumulate significantly lower levels of tryptophan and these plants were used to evaluate if tryptophan might play a role in the regulation of the shikimate pathway. Tubers from trans-genic potatoes also accumulated significantly decreased levels of phenylalanine, accumulated reduced levels of soluble and wall-bound phenolic compounds after wounding and were significantly more susceptible to infection byPhytopthora infestansa major fungal pathogen of potato. The significance of these results will be discussed in relation to the evolution of control architectures in microorganisms, fungi and plants which may regulate the shikimate pathway and which may result in different adaptive responses observed in plants when they accommodate a new artificial metabolic sink.