Leucoanthocyanidin dioxygenase

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).

Table 6.1 Abbreviations BAN, BANYULS bHLH, basic helix-loop-helix CHS, chalcone synthase CHI, chalcone isomerase DFR, dihydroflavonol reductase F3H, flavonol 3-hydroxylase F3 H, flavonoid 3 -hydroxylase FLS, flavonol synthase icx, increased chalcone synthase expression LDOX, leucoanthocyanidin dioxygenase LCR, leucoanthocyanidin reductase MATE, multidrug and toxic compound extrusion NR, not yet reported tt, transparent testa ttg, transparent testa glabrous the WD40 and WRKY transcription factors are named for conserved amino acid sequences within these proteins. PC = personal communication.

PELLETIER, M.K., MURRELL, J., SHIRLEY, B.W., Arabidopsis flavonol synthase and leucoanthocyanidin dioxygenase further evidence for distinct regulation of "early" and "late" flavonoid biosynthetic genes, Plant Physiol., 1997,113, 1437-1445. 

PeUetier MK, MurreU JR, Shirley BW (1997) Characterization of flavonol synthase and leucoanthocyanidin dioxygenase genes in arabidopsis. Further evidence for differential regulation of early and late genes. Plant Physiol 113(4) 1437-1445... 

Stracke R, De Vos RC, Bartelniewoehner L, Ishihara H, Sagasser M, Martens S, Weisshaar B (2009) Metabolomic and genetic analyses of flavonol synthesis in Arabidopsis thaliana support the in vivo involvement of leucoanthocyanidin dioxygenase. Planta 229(2) 427-445... 

Abrahams, S. et al., The Arabidopsis TDS4 gene encodes leucoanthocyanidin dioxygenase (LDOX) and is essential for proanthocyanidin synthesis and vacuole development. Plant Cell, 35, 624, 2003. 

The flavonoid hydroxylases (F3 H, F3 ,5 H) and the phenylpropanoid enzyme cinnamate 4-hydroxylase (C4H) are cytochrome P-450s that are anchored to the cytoplasmic face of the ER.14 F3 H and F3 ,5 H add hydroxyl groups to the 3 and/or 5 of the B ring bringing about chemical and spectral diversity to the flavonoids. Dihydroflavonol 4-reductase (DFR) is the committed step to the production of the precursor of the colored compounds - the leucoanthocyanidins (Fig. 3.2). It is upon the reduction of the 4 keto of the C -ring by DFR (Fig. 3.1) and its further reduction by leucoanthocyanidin dioxygenase/anthocyanidin synthase (LDOX/AS) that the de-localization of the electrons necessary for the formation of the planar flavylium ion is permitted.2... 

Dihydroflavonol 4-reductase (DFR) converted dihydroflavonols (3-OH-flava-nones, 32) to leucoanthocyanidins (flavan-3,4-diols, 37). The leucoanthocyanidins (flavan-3,4-diols, 37) were converted by leucoanthocyanidin dioxygenase (LDOX) to 3-hydroxy-anthocyanidins (38). Finally, 3-hydroxy-antho-cyanidins (38) were converted by three enzymes of O-methyltransferase (OMT), UDPG-flavonoid glucosyl transferase (UFGT) and rhamnosyl transferase (UFGT) to anthocyanins (39) (Fig. 8) [23,24],... 

The biosynthetic pathways of epicatechin (55), cyanidin (51) and proan-thocyanidin (PA) (44) had the same intermediates to leucocyanidin (48). Next, leucoanthocyanidin reductase (LAR) converts the leucocyanidin (48) to epicathechin (55), whereas leucoanthocyanidin dioxygenase (LDOX) converted leucocyanidin (48) to cyanidin (51). Two cyanidin (51) and epicathechin (55) are a precursor of proanthocyanidins (PA) (44). 

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