Engineering budding yeast for the production of coumarins from lignin

As an important renewable resource, lignin has been found difficult to utilize due to its intrinsic heterogeneity. To meet the increasing demand for lignin valorization, in this study we develop novel pathways for coumarins biosynthesis from lignin. Feruloyl-CoA 6'-hydroxylase (F6'H1) and 4-coumarate CoA ligase (4CL) are expressed in budding yeast to produce scopoletin from ferulic acid, which is one of the three main monomers of lignin. Further more, the fusion expression of these two genes enhances the concentration of scopoletin, and the fusion expression with the linker (Gly-Gly-Gly-Gly-Ser)(4) between F6'H1 and 4CL is found to increase scopoletin production by 3.3-fold. In addition, we further develop the conversion pathway from p-coumaric acid to scopoletin by expressing caffeic acid 3-O-methyltransferase (COMT) from different species, because p-coumaric acid is another main monomer of lignin. Ultimately, the engineered budding yeast is applied to convert lignin hydrolysate, and scopoletin titer reaches 4.79 +/- 0.72 mg L-1. This study may serve as a new and efficient approach for lignin valorization and biosynthesis of coumarins.