Biosynthesis and Metabolic Engineering of Proanthocyanidins

Overview

Proanthocyanidins (PAs) are oligomers or polymers of flavan-3-ols widely produced in fern, conifer, and flowering plants. Their presence prevents plants from radiation-caused damage, herbivores, and pathogens. More importantly, flavan-3-ols and oligomeric PAs are potent antioxidative nutrients. Uptake of PAs can protect human beings against cardiovascular diseases, cancer, etc. 

Research efforts have greatly enhanced the understanding of PA biosynthesis in plants.  Our previous work has uncovered a new ANR pathway of PA formation in plants. The new pathway starts with leucoanthocyanidins through anthocyanidins and flavan-3-ols  to PAs. The ANR pathway is featured by the anthocyanidin reductase (ANR) encoded by BANYULS gene (Xie et al, 2003, Science), which has been identified in all investigated plants. The second pathway, called LAR pathway, starts with leucoanthocyanidins through (+)-flavan-3-ols to PAs. This pathway has been molecularly and biochemically demonstrated by the cloning of LAR gene from Desmodium unicinatum and several other plant species. The presence of the LAR pathway in nature still remains to be demonstrated genetically.

Our current studies focus on the polymerization mechanism of PAs. We are using genetic, phytochemical, and cell engineering to clone genes encoding a condensing enzyme involved in polymerization step.