Redirection of tryptophan leads to production of low indole glucosinolate canola

Cruciferous plants are known to produce over a hundred different mustard oil glycosides, which are derived from methionine, phenylalanine, or tryptophan. In oil-producing crops like Brassica napus (canola), the presence of indole glucosinolates in seed protein meals has decreased meal palatability and has limited their value as animal feed. We have transformed canola plants with a gene that encodes tryptophan decarboxylase (TDC) in an attempt to redirect tryptophan into tryptamine rather than into indole glucosinolates. Transgenic plants that expressed this decarboxylase activity accumulated tryptamine while correspondingly lower levels of tryptophan-derived indole glucosinolates were produced in all plant parts compared with nontransformed controls. Of particular significance, the indole glucosinolate content of mature seeds from transgenic plants was only 3% of that found in nontransformed seeds. These results demonstrate how the creation of artificial metabolic sinks could divert metabolite flow and be used to remove these undesirable indole glucosinolates, thereby increasing the value of the oilseed meals, which are produced after extraction of oil from the seed.