Biosynthetic pathway of CPT from DMAPP to strictosidine and from strictosidine to CPT in C. acuminata. (A) The upstream pathway for the synthesis of backbone strictosidine. (B) The proposed branch pathway of CPT biosynthesis (steps after strictosidine synthesis). TSB: β-subunit of tryptophan synthase; TDC: tryptophan decarboxylase; G10H: geraniol-10-hydroxylase; SCS: secologanin synthase; STR: strictosidine synthase; 10-HGO: 10-hydroxy geraniol oxidoreductase. PGD: putative strictosidine β-D-glucosidase. The arrow with the dotted shaft represents the step that was presumed in the study to be catalyzed by a CYP450.