Figure 5. Proposed biosynthetic pathways of three major types of BIA identified from Dichocarpum species.

The common route of BIA biosynthesis is highlighted in orange, routes leading to protoberberine, aporphine and bis-BIA are shown in blue, purple and green, respectively. The major intermediates are marked by red circles. C-O and C-C coupling reactions could be catalyzed by CYP80 family members. Cleavage of the methylenedioxy bridge could be catalyzed by CYP via hydroxylation of the methylenedioxy carbon, followed by decomposition to the catechol metabolite and formic acid (Richards et al., 2019). The meaning of abbreviations is shown in Table S5.