Biosynthesis of Plant Triterpenoid Saponins in Microbial Cell Factories

Triterpenoid saponins are triterpenoid glycoside compounds which have been widely used in pharmaceutical, agricultural, and food industries. Traditionally, they are extracted from plants, which is time-consuming and environmentally unfriendly. Recently, de novo synthesis of triterpenoid saponins in microbial cell factories was realized, which provides a promising and green approach to alter the traditional supply way. However, the complex biosynthetic pathway and the poor suitability between the endogenous and heterogeneous pathways tremendously limit the yield of triterpenoid saponins. We introduce the biosynthetic pathways of triterpenoid saponins first, and we then summarize the microbial cell factories developed to produce these compounds. Further, we discuss the strategies applied to enhance the production. This paper systematically illustrates the biosynthesis of plant triterpenoid saponins in microbial cell factories.