Syringyl monolignols

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. 

In our analysis of the chemical structures which are active tur-inducers (41) it was found that the compounds fell into four groups (1) acetophenones and related structures, (2) monolignols, (3) hydroxycinnamic acids and their esters, and (4) chalcone derivatives (Fig. 1). Each compound had either a guaiacyl or a syringyl nucleus, and with the exception of the monolignols, possessed a carbonyl group. Most were of common occurrence in vascular plants. 

As briefly described above, proposed biosynthetic pathways to the monolignols follow a metabolic grid, with a number of parallel and redundant pathways for the synthesis of the major lignin components, namely guaiacyl and syringyl units. Currently, the methylation steps in the lignin biosynthetic pathway are believed to follow two main branches dependent on COMT and CCoAOMT,... 

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. 

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. 

Syringyl Lignin Pathways Two key enzymes (beyond the coniferyl alcohol pathway) are required for the production of sinapyl alcohol, which is the essential monolignol for production of syringyl units in lignins. Ferulate 5-hydroxylase, FH5, now perhaps more appropriately called CAld-5H to reflect coniferaldehyde as the preferred substrate [347,348], effects the 5-hydroxylation. Caffeate 0-methyltransferase,... 

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