Fig. 1

The biosynthetic pathway of steviol constructed in a heterologous host, E. coli. IPP, the precursor of steviol, is synthesized by the endogenous MEP pathway of E. coli. FPP is converted to steviol by the exogenous steviol synthesis pathway. Single arrows represent single-step reactions, while triple arrows denote multistep reactions. Red arrows indicate overexpressed genes intended to enhance the precursor pool. The genes (dxs from Bacillus subtilis, dxr from E. coli, and idi and ispA from Enterococcus sp.) were integrated into the genome of the MG1655 strain. CDPS, ent-copalyl diphosphate synthase; CPR, NADPH–cytochrome P450 reductase; DMAPP, dimethylallyl pyrophosphate; DXP, 1-deoxy-d-xylulose 5-phosphate; DXR, 1-deoxy-d-xylulose 5-phosphate reductoisomerase; DXS, 1-deoxyxylulose-5-phosphate synthase; FPP, farnesyl diphosphate; G3P, glyceraldehyde-3-phosphate; GPP, geranyl diphosphate; GGPPS, geranylgeranyl diphosphate synthase; IDI, isopentenyl diphosphate isomerase; IPP, isopentenyl pyrophosphate; IspA, farnesyl diphosphate synthase; KAH, kaurenoic acid 13-hydroxylase; KO, ent-kaurene oxidase; KS, ent-kaurene synthase; MEP, 2-C-methylerythritol 4-phosphate; Pyr, pyruvate