Biosynthesis and Metabolic Engineering of PProanthocyanidins Projects
Proanthocyanidins (PAs) are oligomers or polymers of flavan-3-ols and are widely produced in fern, conifer, and flowering plants. Their presence protects plants from radiation-induced damage, herbivores, and pathogens. More importantly, flavan-3-ols and oligomeric PAs are potent antioxidative nutrients. Uptake of these natural PAs can protect human beings against cardiovascular diseases, cancer, etc. The levels and structures of PAs are very important agronomic traits of many fruit products (e.g. strawberry, apple, blueberry, grape etc). Increasing the bioavailable monomers and oligomeric PAs in these fruit products can improve nutritional values to benefit human health.
Recent efforts have greatly enhanced the understanding of PA biosynthesis in plants. Our previous work uncovered a new pathway of PA formation in plants. The new pathway , called ANR pathway, starts with leucoanthocyanidins through anthocyanidins and flavan-3-ols to PAs, The ANR pathway is featured in the anthocyanidin reductase (ANR) encoded by BANYULS gene firstly identified in Arabidopsis thaliana (Xie et al, 2003, Science). The pathway has been found in all investigated plants. The second pathway, called LAR pathway, also starts with leucoanthocyanidins through (+)-flavan-3-ols to PAs. This pathway has been molecularly and biochemically demonstrated by the cloning of the LAR gene from Desmodium unicinatum, but the presence of this pathway in nature still needs genetic evidence.
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.