Flavonoids: biosynthesis, biological functions, and biotechnological applications

Abstract

Flavonoids are widely distributed secondary metabolites with different metabolic functions in plants. The elucidation of the biosynthetic pathways, as well as their regulation by MYB, basic helix-loop-helix (bHLH), and WD40-type transcription factors, has allowed metabolic engineering of plants through the manipulation of the different final products with valuable applications. The present review describes the regulation of flavonoid biosynthesis, as well as the biological functions of flavonoids in plants, such as in defense against UV-B radiation and pathogen infection, nodulation, and pollen fertility. In addition, we discuss different strategies and achievements through the genetic engineering of flavonoid biosynthesis with implication in the industry and the combinatorial biosynthesis in microorganisms by the reconstruction of the pathway to obtain high amounts of specific compounds.

Keywords: combinatorial biosynthesis; defense; flavonoid; genetic engineering; transcription factors.

Figure 1

Structure of the main classes of flavonoids.

Figure 2

Regulation of the flavonoid pathway in Arabidopsis thaliana (A) and maize (B). Enzymes and intermediates are indicated in black and different regulators are indicated in color. End products are identified in capital letters. Dotted arrows indicate multiple steps. CHS, Chalcone synthase; CHI, chalcone isomerase; F3H, flavanone 3-hydroxylase; F3′H, flavonoid-3′-hydroxylase; DFR, dihydroflavonol 4-reductase; FNR, flavanone 4-reductase; ANS, anthocyanidin synthase; UFGT, UDP-glucose flavonoid 3-O glucosyltransferase; FLS, flavonol synthase; LAR, leucoanthocyanidin reductase; ANR, anthocyanidin reductase.

Figure 3

Biosynthesis of anthocyanidins: cyanidin, pelargonidin and delphinidin. The simplified scheme comprises the anthocyanidin branch and other flavonoid end products (flavonols and flavones). The enzymes catalyzing each step are indicated in bold. CHS, Chalcone synthase; CHI, chalcone isomerase; FNS, flavone synthase; F3H, flavonoid-3-hydroxylase; F3′H, flavonoid-3′-hydroxylase; F3′5′H, flavonoid 3′,5′-hydroxylase; FLS, flavonol synthase; DFR, dihydroflavonol 4-reductase; ANS, anthocyanidin synthase. The pictures of flowers correspond to (left to right): Chrysanthemum morifolium, pink gentian (Gentiana scabra), Calendula officianalis, Ipomoea quamochit, blue gentian (Gentiana triflora) and Evolvulus pilosus.