Learning from plants – Microbial production of plant specialized compounds

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 natural defense system of plants 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 cancer-preventive properties of broccoli [1].

GRN is derived from methionine that first undergoes a series of four enzymatic reactions to form the chain-elongated dihomo-methionine (DHM). Subsequently, DHM is converted into GRN by a cytosolic seven-step pathway [2]. We have demonstrated the feasibility to engineer the 13-step pathway 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. We successfully transferred the pathway for the tryptophan-derived indole GLs by stable integration into the genome of S. cerevisiae [4]. Recently, we succeeded in producing DHM, the precursor for GRN, in E. coli. We are currently implementing the full pathway into our two expression systems to evaluate the most promising production host.

References:

[1] Juge N, et al., Molecular basis for chemoprevention by sulforaphane: a comprehensive review. Cellular and Molecular Life Sciences, 2007 64: 1105 – 1127.

[2] Sonderby I.E, Geu-Flores F, Halkier BA, Biosynthesis of glucosinolates–gene discovery and beyond. Trends Plant Sci, 2010 15: 283 – 90.

[3] Mikkelsen MD, Olsen CE, Halkier BA, Production of the cancer-preventive glucoraphanin in tobacco. Mol Plant 2010 3: 751 – 9.

[4] Mikkelsen MD, et al., Microbial production of indolylglucosinolate through engineering of a multi-gene pathway in a versatile yeast expression platform. Metabolic Engineering, 2012. 14: 104 – 111.