Video Upload Options

Flavonoid biosynthesis is a multi-enzyme metabolic pathway in plants that produces flavonoids, a large class of polyphenolic secondary metabolites characterized by a C6–C3–C6 carbon skeleton ^[1]. The pathway originates from the phenylpropanoid branch of primary metabolism, in which the amino acid phenylalanine is converted to cinnamic acid by phenylalanine ammonia-lyase (PAL), subsequently hydroxylated by cinnamate-4-hydroxylase (C4H) and activated to p-coumaroyl-CoA by 4-coumarate-CoA ligase (4CL) ^[2]. The committed step of flavonoid biosynthesis is catalyzed by chalcone synthase (CHS), a type III polyketide synthase that condenses p-coumaroyl-CoA with three molecules of malonyl-CoA to yield naringenin chalcone, the foundational scaffold for all flavonoid subclasses ^[3]. Chalcone isomerase (CHI) then catalyzes the intramolecular cyclization of chalcone to the flavanone naringenin, from which the pathway diverges into multiple branches through the action of downstream enzymes including flavonoid 3′-hydroxylase, flavonoid 3′,5′-hydroxylase, flavanone 3-hydroxylase, dihydroflavonol 4-reductase, anthocyanidin synthase, and anthocyanidin reductase. These enzymatic steps generate the eight major flavonoid branches—stilbene, aurone, flavone, isoflavone, flavonol, phlobaphene, proanthocyanidin, and anthocyanidin—each distinguished by specific hydroxylation, methylation, glycosylation, and oxidation patterns ^[1]. The pathway is subject to multilayered transcriptional regulation, primarily mediated by MYB–bHLH–WD40 transcription factor complexes that coordinate tissue-specific, developmental, and environmentally responsive expression of structural genes ^[4]. Genomic analyses have revealed that flavonoid biosynthetic genes have evolved through gene duplication and functional divergence, with enzyme families such as cytochrome P450 monooxygenases, short-chain dehydrogenases/reductases, and 2-oxoglutarate-dependent dioxygenases acquiring specialized roles in modifying the flavonoid scaffold ^[5].