Fig. 1: A plausible biosynthesis pathway of echinacoside.

a Cistanche tubulosa plant in desert. b Skeleton of PhG compounds. c Chemical structure of echinacoside (ECH). d Three possible upstream pathways for tyrosol or hydroxytyrosol biosynthesis, including the TyDC-TYO-ADH pathway (pathway 1), AAS-ADH pathway (pathway 2) and TAT-PPDC-ADH pathway (Ehrlich pathway, pathway 3) that are shown in different colours. e Downstream pathways involving the assembling of acyl, hydroxyl, rhamnosyl, and glucosyl modules in the biosynthesis of ECH.