Pathway enzyme engineering for flavonoid production in recombinant microbes

Metabolic engineering of microbial strains for the production of flavonoids of industrial interest has attracted great attention due to its promising advantages over traditional extraction approaches, such as independence of plantation, facile downstream separation, and ease of process and quality control. However, most of the constructed microbial production systems suffer from low production titers, low yields and low productivities, restricting their commercial applications. One important reason of the inefficient production is that the expression conditions and the detailed functions of the flavonoid pathway enzymes are not well understood. In this review, we have collected the biochemical properties, structural details, and genetic information of the enzymes in the flavonoid biosynthetic pathway as a guide for the expression and analysis of these enzymes in microbial systems. Additionally, we have summarized the engineering approaches used in improving the performances of these enzymes in recombinant microorganisms. Major challenges and future directions on the flavonoid pathway are also discussed.