Biosynthesis of anthocyanins

Recently, a new polyketide biosynthetic pathway in bacteria that parallels the well studied plant PKSs has been discovered that can assemble small aromatic metabolites.8,9 These type III PKSs10 are members of the chalcone synthase (CHS) and stilbene synthase (STS) family of PKSs previously thought to be restricted to plants.11 The best studied type III PKS is CHS. Physiologically, CHS catalyzes the biosynthesis of 4,2, 4, 6 -tetrahydroxychalcone (chalcone). Moreover, in some organisms CHS works in concert with chalcone reductase (CHR) to produce 4,2 ,4 -trihydroxychalcone (deoxychalcone) (Fig. 12.1). Both natural products constitute plant secondary metabolites that are used as precursors for the biosynthesis of anthocyanin pigments, anti-microbial phytoalexins, and chemical inducers of Rhizobium nodulation genes.12... 

Joung, J.Y. et al., An overexpression of chalcone reductase of Pueraria montana var. lobata alters biosynthesis of anthocyanin and 5 -deoxyflavonoids in transgenic tobacco. Biochem. Biophys. Res. Common., 303, 326, 2003. 

Saito, K. and Yamazaki, M., Biochemistry and molecular biology of the late-stage of biosynthesis of anthocyanin lessons from Perilla frutescens as a model plant. New Phytol, 155, 9, 2002. 

The inheritance and biosynthesis of anthocyanin pigmentation in Petunia and Solanum have received immense interest throughout many decades, and the first experiments in genetically modifying anthocyanin flower color were carried out on Petunia hybrida. ... 

Figure 3-8. Biosynthesis of anthocyanins and condensed tannins. The enzymes involved in this pathway are (a) anthocyanidin synthase (E.C. 1.14.11.19), (b) anthocyanin 3-glycosyl transferase, and (c) BANYULS.

Interestingly, regulatory genes involved in the biosynthesis of anthocyanins were identified relatively early on. This was possible because of a number of mutants that accumulated high levels of anthocyanins, or that accumulated anthocyanins in tissues where they were normally not found, in combination with the easily scorable phenotype of these mutants. 

Li H, Flachowsky H, Fischer T, Hanke M-V, Forkmann G, Treutter D, Schwab W, Hoffmann T, Szankowski I. 2007. Maize Lc transcription factor enhances biosynthesis of anthocyanins, distinct proanthocyanidins and phenylpropanoids in apple (Malus domestica Borkh.) Planta 226 1243-1254. 

Fig. 8 Biosynthesis of anthocyanins (39) via leucoanthocyanidins (flavan-3,4-diols, 37) from dihydroflavonols (3-hydroxy-flavanones, 31, 32)...

Anthocyanins accumulate relatively late in the maturation process of fruits. CA conditions, which delay maturation, can thus be expected to delay the development of anthocyanin pigments. This may be mediated through reduced sensitivity to C2H4, which has been shown to accelerate biosynthesis of anthocyanins (39.411. CA conditions can also alter cellular pH in plant tissues (421 and consequently induce changes in anthocyanins. 

Fraits with a marked de novo biosynthesis of anthocyanins (i.e., grape, apple, olive, pomegranate, red cherry, raspberry, cranberry, etc.). 

Biosynthesis of C-Glycosyl Flavonoids Biosynthesis of Anthocyanins Systematic Studies with Flavone and Flavonol Glycosides Biological Activity of Flavone and Flavonol Aglycones and Glycosides... 

Tomato Antirrhinum/ overexpression CaMV35S/ )e/ E)elila Myc TFs that activate biosynthesis of anthocyanin Higher anthocyanins in mature leaves (23-fold), corolla (40-fold), and stamen (50-fold) but no change in fruit [76]... 

Anthocyanidin synthase (ANS), the key enzyme in the biosynthesis of anthocyanins, catalyzes oxidation of leucoanthocyanidin (flavan-3,4-diol) to a 2-flaven-3,4-diol that spontaneously isomerizes to 3-flaven-2,3-diol (anthocyanidin) (Fig. 5). This is subsequently glycosylated at C-3, transported to the vacuole, and finally converted to the colored flavilium cation at the acidic... 

Dihydroflavonol 4-reductase (DFR) is involved in the biosynthesis of anthocyanins and proanthocyanidins (PAs). DFRs catalyze the stereospecific reduction of (2R,3R)-dihydrofla-vonols to (2R,3R,45)-leucoanthocyanidins [77] (Fig. 5). Petunia possesses three different DFR genes (dfrA-C), but only dfrA is transcribed in floral tissues. DFR-A does not accept dihy-drokaempferol, the precursor for the synthesis of pelar-gonidin-type anthocyanins. Consequently, no orange-colored petunia flowers are foimd in nature [89]. Dihydroquercetin and (hhydramyrice-tin are also substrates for DFRs and provide leu-cocyanidin and leucodelphinidin, respectively. 

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