Microbial production of the cancer-preventive glucosinolate Glucoraphanin – Nicotiana benthamiana as tool to alleviate bottle necks in metabolic engineering

Abstract

Glucosinolates (GLs) are specialized bioactive compounds characteristic of plants in the order Brassicales, including the model plant Arabidopsis thaliana. GLs are key players in the plant's natural defense system against herbivores and microorganisms. Additional biological functions range from flavor compounds to bio-pesticides. Particularly, glucoraphanin (GRN), the major glucosinolate in broccoli has been associated with broccoli's cancer-preventive properties [1]. GRN is derived from methionine that first undergoes a series of four enzymatic reactions to form the chain-elongated dihomomethionine. Methionine chain-elongation is partially compartmentalized to the chloroplast. Subsequently, dihomomethionine is converted into GRN by a cytosolic seven-step pathway [2]. Recently, we have demonstrated the feasibility to engineer the 13-step pathway of GRN biosynthesis from A. thaliana into the non-cruciferous plant species Nicotiana benthamiana by transient expression [3]. The goal is to ultimately transfer the GRN pathway into a microbial host organism for sustainable production. As proof-of-concept we successfully transferred the pathway for the simple tryptophan-derived indole GLs by stable integration of seven biosynthetic and one supporting gene into the genome of S. cerevisiae [4].