A Rehmannia glutinosa caffeic acid O‐methyltransferase functional identification: Reconstitution of the ferulic acid biosynthetic pathway in Saccharomyces cerevisiae using Rehmannia glutinosa enzymes

Rehmannia glutinosa produces many pharmacological natural components, including ferulic acid (FA) which is also an important precursor of some medicinal ingredients, so it is very significant to explore FA biosynthesis for enhancing the production of FA and its derivations. This study aimed to determine and reconstitute the R. glutinosa FA biosynthetic pathway from phenylalanine (Phe) metabolism in Saccharomyces cerevisiae as a safe host for the biosynthesis of plant-derived products. Although plant caffeic acid O-methyltransferases (COMTs) are thought to be a vital catalytic enzyme in FA biosynthesis pathways, to date, none of the RgCOMTs in R. glutinosa has been characterized. This study identified an RgCOMT and revealed its protein enzymatic activity for FA production in vitro. The RgCOMT overexpression in R. glutinosa significantly increased FA yield, suggesting that its molecular function is involved in FA biosynthesis. Heterologous expression of the RgCOMT and reported R. glutinosa genes, RgPAL2 (encoding phenylalanine ammonia-lyase [PAL] protein), RgC4H (cinnamate 4-hydroxylase [C4H]), and RgC3H (p-coumarate-3-hydroxylase [C3H]), in S. cerevisiae confirmed their catalytic abilities in the reaction steps for the FA biosynthesis. Importantly, in this study, these genes were introduced into S. cerevisiae and coexpressed to reconstitute the R. glutinosa FA biosynthetic pathway from Phe metabolism, thus obtaining an engineered strain that produced an FA titer of 148.34 mg L-1 . This study identified the functional activity of RgCOMT and clarified the R. glutinosa FA biosynthesis pathway in S. cerevisiae, paving the way for the efficient production of FA and its derivatives.