Leucoanthocyanidin reductase plants

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).

DFR belongs to the single-domain-reductase/epimerase/dehydrogenase (RED) protein family, which has also been termed the short chain dehydrogenase/reductase (SDR) superfamily. This contains other flavonoid biosynthetic enzymes, in particular the anthocyanidin reductase (ANR), leucoanthocyanidin reductase (EAR), isoflavone reductase (IFR), and vestitone reductase (VR), as well as mammalian, bacterial, and other plant enzymes. ... 

Bogs J, Downey MO, Harvey JS, Ashton AR, Tanner GJ, Robinson SP. 2005 Proanthocyanidin synthesis and expression of genes encoding leucoanthocyanidin reductase and anthocyanidin reductase in developing grape berries and grapevine leaves. Plant Physiol 139 652-663. 

Tanner GJ, Franki KT, Abrahams S, Watson JM, Larkin PJ, Ashton AR. 2003. Proanthocyanidin biosynthesis in plants Purification of legume leucoanthocyanidin reductase and molecular cloning of its cDNA. J Biol Chem 278 31647-31656. 

Flavan-3,4-diols FIavan-3,4-diols, also known as leucoanthocyanidins, are not particularly prevalent in the plant kingdom, instead being themselves precursors of flavan-3-ols (catechins), anthocyanidins, and condensed tannins (proanthocyanidins) (see Fig. 5.4). Flavan-3,4-diols are synthesized from dihydroflavonol precursors by the enzyme dihydroflavonol 4-reductase (DFR), through an NADPH-dependent reaction (Anderson and Markham 2006). The substrate binding affinity of DFR is paramount in determining which types of downstream anthocyanins are synthesized, with many fruits and flowers unable to synthesize pelargonidin type anthocyanins, because their particular DFR enzymes cannot accept dihydrokaempferol as a substrate (Anderson and Markham 2006). 

Dihydroflavonol 4-reductase (DFR EC 1.1.1.219) is a member of the short-chain dehydrogenase/reductase family and catalyzes the stereospecific conversion of (+)-(2R,3R)-dihydroflavonols to the corresponding (2R,3S,4S) flavan-3,4-cw-diols (leucoanthocyanidins), with NADPH as a required cofactor. The enzyme activity was first identified in cell suspension cultures of Douglas fir (Pseudotsuga menziesii) and was shown to be related to the accumulation of flavan-3-ols and proanthocyanidins [96]. Leucoanthocyanidins and DFR were later shown to be required for anthocyanidin formation by complementation of Matthiola incana mutants blocked between dihydroflavonol and anthocyanidin biosynthesis [97, 98], DFR has been purified to apparent homogeneity and biochemically analyzed from flower buds of Dahlia variabilis [99]. DFR was shown to accept different substrates depending on the plant species from which it was isolated (reviewed in 100). 

Paolocci F, Robbins MP, Madeo L, Arcioni S, Martens S, Damiani F. 2007. Ectopic expression of a basic helix-loop-helix gene transactivates parallel pathways of proanthocyanidin biosynthesis. Structure, expression, analysis, and genetic control of leucoanthocyanidin 4-reductase and anthocyanidin reductase genes in Lotus corniculatus. Plant Physiol 143 504-516. 

Pfeiffer J, Kiihnel C, Brandt J, Duy D, Punyasiri PA, Forkmann G, Fischer TC. 2006. Biosynthesis of flavan 3-ols by leucoanthocyanidin 4-reductases and anthocyanidin reductases in leaves of grape (Vitis vinifera L.), apple (Malus x domestica Borkh.) and other crops. Plant Physiol Biochem 44 323-334. 

The reduction of 3-hydroxyflavones (dihydroflavanols) to 3,4-diols (leucoanthocyanidins) was first demonstrated in cell-free extracts of Pseudotsuga menziesii and Ginkgo bi-loba, by the reduction of (-I- )-dihydroquercetin with dihy-droflavonol 4-reductase in the presence of NADPH to a 2,3-trans-3,4-cis-diol which differs from the product of nonen-zymatic reduction, 2,3-trans-3,4-trans-diol (2R,3S,4R)-(+ )-3,4,5,7,3, 4 -hexahydroxyflavan (Fig. 11.15 of Chapter 11). This result has now been confirmed in several other plant systems (Heller and Forkmann, 1988 Stafford, 1989). 

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