Biosynthesis of £-monolignols

Boerjan W, Ralph J, Baucher M (2003) Lignin biosynthesis. Annu Rev Plant Biol 54 519-546 Dixon RA, Reddy MSS (2003) Biosynthesis of monolignols. Genomic and reverse genetic approaches. Phytochem Rev 2 289-306... 

The reduction of />coumaroyl-CoA (3.31) to />coumaryl aldehyde (3.69) is catalyzed by the enzyme cinnamoyl-CoA NADP oxidoreductase (CCR). This enzyme was initially purified from soybean cultures (Wegenmayer et al., 1976), and was later on efficiently isolated from lignifying cambium of eucalyps (Eucalyptus gunnii) (Gofifiier et al., 1994). A CCR cDNA was identified in a cDNA library that was screened with oligonucleotiede derived from the peptide sequence of the CCR protein. CCR is considered the first enzyme committed towards the biosynthesis of monolignols and shows... 

Figure 3-9. Biosynthesis of monolignols. The enzymes involved in this pathway are ( ) hydroxycinnamoyl-CoA shikimate/quinate hydroxy-cinnamoyl transferase, (b) p-coumaroyl-CoA 3 -hydroxylase (E.C. 1.14.14.1), (c) caffeoyl-CoA O-methy 1 Iranslerasc (E.C. 2.1.1.104), (d) cinnamoyl-CoA reductase (E.C. 1.2.1.44) (e) cinnamyl alcohol dehydrogenase (E.C. 1.1.1.195), (f) coniferyl aldehyde/coniferyl alcohol 5-hydroxylase (E.C. 1.14.13), (g) coniferaldehyde/coniferyl alcohol O-methyltransferase (E.C. 2.1.1.68).

Davin, F.B. and Lewis, N.G. (1992) Phenylpropanoid metabolism biosynthesis of monolignols, lignans and neolignans, lignins and suberins, in Phenolic Metabolism in Plants (eds H.A. Stafford and R.K. Ibrahim). Plenum, New York, pp. 325-75. 

Dixon, R.A., Ghen, R, Guo, D. and Parvathi, K. (2001) The biosynthesis of monolignols a metabolic grid, or independent pathways to guaiacyl and syringyl units Phytochemistry, 57,1069-84. 

L. B. Davin N. G. Lewis, Phenylpropanoid Metabolism Biosynthesis of Monolignols, Lignans and Neolignans, Lignins and Suberins. In Recent Advances in Phytochemistry] Vol. 26 Phenolic Metabolism in Plants H. A. Stafford, R. K. Ibrahim, Eds. Plenum Press New York, 1992 pp 325-375. 

Li, L. Popko, J. L. Umezawa, T. Chiang, V. L. 5-Hydroxyconiferyl aldehyde modulates enzymatic methylation for syringyl monolignol formation, a new view of monolignol biosynthesis in angiosperms. J. Biol. Chem. 2000, 275, 6537-6545. 

Onnerud, H. Zhang, L. Gellerstedt, G. Henriksson, G. Polymerization of monolignols by redox shuttle-mediated enzymatic oxidation a new model in lignin biosynthesis I. Plant Cell 2002, 14, 1953-1962. 

Validation of the role of femloyl-CoA in the synthesis of the vanillin precursor will be detection of the appropriate intermediates and/or enzyme activities in placental extracts that could account for the production of the predicted levels of capsaicinoids. The presence of low levels of monolignol intermediates could be explained by lignin biosynthesis. An alternate route from phenylalanine to vanillin has been considered by some investigators Orlova et al. [68] demonstrated the role of the benzenoid pathway in petunia flowers for the biosynthesis of phenylpropanoid/benzenoid volatiles. 

Reviews that include aspects of monolignol biosynthesis have been published by, e.g., Lewis and Yamamoto (1990), Davin and Lewis (1992), Whetten and Sederoff (1995), Boudet (1998), Van Rensburg et al. (2000), Dixon et al. (2001), Anterola and Lewis (2002), Boerjan et al. (2003) and Davin and Lewis (2003), Dixon and Reddy (2003), Goujon et al. (2003b), Chiang (2006). 

Anterola, A.M., Jeon, J.Fi., Davin, L.B. and Lewis, N.G. (2002) Transcriptional control of monolignol biosynthesis in Pinus taeda. Factors affecting monolignol ratios and carbon allocation in phenylpropanoid metabolism. /. Biol. Chem., 277, 18272-80. 

Boudet, A.M., Goffner, D., Marque, C. and Grima-Pettenati, J. (1998) Genes involved in the final steps of monolignol biosynthesis and their manipulation for tailoring new lignins. ACS Symp. Ser., 697,65-75. 

Chen, R, Reddy, M.S.S., Temple, S., Jackson, L., Shadle, G. and Dixon, R.A. (2006) Multi-site genetic modulation of monolignol biosynthesis suggests new routes for formation of syringyl lignin and wall-bound ferulic acid in alfalfa Medicago sativa L.). Plant., 48, 113-24. 

Lewis, N.G. and Davin, L.B. (1998) The biochemical control of monolignol coupling and structure during lignan and lignin biosynthesis. ACS Symp. Sen, 697, 334—61. 

Li, L., Cheng, X., Lu, S., Nakatsubo, T, Umezawa, T. and Chiang, V.L. (2005) Clarification of cinnamoyl co-enzyme A reductase catalysis in monolignol biosynthesis of aspen. Plant Cell Physiol, 46, 1073-82. 

Such products implicate the biosynthesis of sinapyl y-acetate as a precursor of Kenaf lignin (see Novel Mono-tetrahydrofurans Provide Evidence that Acylated Monolignols are True Lignin Precursors section) [101,260]. The functional role of such high levels of acetates in kenaf lignins awaits explanation. Although present at much lower levels, except in palms where they may be substantial [323], acetates on the y-position have been confirmed in aspen by a modified DFRC analysis [312]. Detailed NMR studies elucidating the nature of these minor acetate levels have not been carried out. 

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