Flavonoid biosynthesis pathway

Schijlen EWGM, de Vos CHR, Martens S, Jonker HH, Rosin FM, Molthoff JW, Tikunov YM, Angenent GC, van Tunen AJ, Bovy AG (2007) RNA interference silencing of chalcone synthase, the first step in the flavonoid biosynthesis pathway, leads to parthenocarpic tomato fruits. Plant Physiol 144 1520-1530... 

The precursors of flavonoid biosynthesis include shikimic acid, phenylalanine, cinnamic acid, and p-coumaric acid. Shikimic acid acts as an intermediate in the biosynthesis of aromatic acid. The basic pathways to the core isoflavonoid skeletons have been established both enzymatically and genetically [16]. The synthesis of isoflavones can be broadly divided into three main synthetic pathways the formylation of deoxybenzoins, the oxidative rearrangement of chalcones and flavanones, and the arylation of a preformed chromanone ring. In leguminous plants, the major isoflavonoids are produced via two branches of the isoflavonoid biosynthetic pathway, and the different branches share a majority of common reactions [1]. Unlike the common flavonoid compotmds, which have a 2-phenyl-benzopyrone core structure, isoflavones, such as daidzein and genistein, are 3-phenyl-benzopyrone compounds. Biochemically, the synthesis of isoflavones is an offshoot of the flavonoids biosynthesis pathway. Several attempts have aimed to increase... 

Biosynthesis of Tea Flavonoids. The pathways for the de novo biosynthesis of flavonoids in both soft and woody plants (Pigs. 3 and 4) have been generally elucidated and reviewed in detail (32,51). The regulation and control of these pathways in tea and the nature of the enzymes involved in synthesis in tea have not been studied exhaustively. The key enzymes thought to be involved in the biosynthesis of tea flavonoids are 5-dehydroshikimate reductase (52), phenylalanine ammonia lyase (53), and those associated with the shikimate/arogenate pathway (52). At least 13 enzymes catalyze the formation of plant flavonoids (Table 4). 

Poly(3HB) synthesis in various subcellular compartments could be used to study how plants adjust their metabolism and gene expression to accommodate the production of a new sink, and how carbon flux through one pathway can affect carbon flux through another. For example, one could study how modifying the flux of carbon to starch or lipid biosynthesis in the plastid affects the flux of carbon to acetyl-CoA and poly(3HB). Alternatively, one could study how plants adjust the activity of genes and proteins involved in isoprenoid and flavonoid biosynthesis to the creation of the poly(3HB) biosynthetic pathway in the cytoplasm, since these three pathways compete for the same building block, i. e., acetyl-CoA. 

Ring B and the central three-carbon bridge forming the C ring (see Fig. 5.1) originate from the amino acid phenylalanine, itself a product of the shikimate pathway, a plastid-based process which generates aromatic amino acids from simple carbohydrate building blocks. Phenylalanine, and to a lesser extent tyrosine, are then fed into flavonoid biosynthesis via phenylpropanoid (C6-C3) metabolism (see Fig. 5.1). 

Figure 6.1 Major branch pathways of flavonoid biosynthesis in Arabidopsis. Branch pathways, enzymes, and end products present in other plants but not Arabidopsis are shown in light gray. Abbreviations cinnamate-4-hydroxylase (C4H), chalcone isomerase (CHI), chalcone synthase (CHS), 4-coumarate CoA-ligase (4CL), dihydroflavonol 4-reductase (DFR), flavanone 3-hydroxylase (F3H), flavonoid 3 or 3 5 hydroxylase (F3 H, F3 5 H), leucoanthocyanidin dioxygenase (LDOX), leucoanthocyanidin reductase (LCR), O-methyltransferase (OMT), phenylalanine ammonia-lyase (PAL), rhamnosyl transferase (RT), and UDP flavonoid glucosyl transferase (UFGT).

Punyasiri PA, Abeysinghe IS, Kumar V, Treutter D, Duy D, Gosch C, Martens S, Eorkmann G, Fischer TC (2004) Flavonoid biosynthesis in the tea plant Camellia sinensis properties of enzymes of the prominent epicatechin and catechin pathways. Arch Biochem Biophys 431(l) 22-30... 

The key enzymes involved in the formation of the hydroxycinnamic acids (HCAs) from phenylalanine and malonyl-CoA are now discussed in detail, while later sections address the branches of the flavonoid pathway leading to anthocyanins, aurones, flavones, flavonols, PAs, and isotlavonoids. This is followed by brief reviews of the regulation of flavonoid biosynthesis and the use of flavonoid genes in plant biotechnology. To assist the reader. Figure 3.1 presents the carbon numbering for the various flavonoid types discussed. 

Coumaroyl-CoA is produced from the amino acid phenylalanine by what has been termed the general phenylpropanoid pathway, through three enzymatic conversions catalyzed by phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), and 4-coumarate CoA ligase (4CL). Malonyl-CoA is formed from acetyl-CoA by acetyl-CoA carboxylase (ACC) (Figure 3.2). Acetyl-CoA may be produced in mitochondria, plastids, peroxisomes, and the cytosol by a variety of routes. It is the cytosolic acetyl-CoA that is used for flavonoid biosynthesis, and it is produced by the multiple subunit enzyme ATP-citrate lyase that converts citrate, ATP, and Co-A to acetyl-CoA, oxaloacetate, ADP, and inorganic phosphate. ... 

Figure 3-7. Flavonoid biosynthesis (this page and next page). The enzymes involved in this pathway are (a) chalcone synthase (E.C. 2.3.1.73), (b) aureusidin synthase (E.C. 1.21.3.6), (c) chalcone isomerase (E.C. 5.5.1.6), (d) flavanone 3-hydroxylase (E.C. 1.14.11.9), (e) flavone synthase (E.C. 1.14.11.22), (f) flavonoid 3 -hydroxylase (E.C. 1.14.13.21),...

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