Fig. 2

Biosynthetic pathway of lignans in I. indigotica. Lignin and lignans come from caffeoyl-CoA, which could be produced from p-coumaric acid through caffeic acid or from p-coumaroyl-CoA through the CoASH-shikimate cycle. Active lignans and their corresponding derivatives in I. indigotica initiate from the dimerization of coniferyl alcohol. Blue and gray routes indicate different biosynthetic pathway leading to caffeoyl-CoA. The figure is adapted from Xiao et al. (2015) and Chen et al. (2021b)