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Title: ESSENTIAL ROLE OF CAFFEOYL COENZYME A O-METHYLTRANSFERASE IN LIGNIN

Author
item ZHONG, RUIQIN - DEPT OF BOT UNIV OF GA
item Morrison Iii, Wiley
item Himmelsbach, David
item Poole, Farris
item YE, ZHENG-HUA - DEPT OF BOT UNIV OF GA

Submitted to: Phytochemistry
Publication Type: Review Article
Publication Acceptance Date: 6/12/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Lignin is a complex polymer found mainly in walls of plants and contributes to plant rigidity. Lignin, which contributes up to 15 - 35% of the dry weight of wood, ranks the second most abundant biomass on earth after cellulose. A target of the research discussed has been understanding how lignin is formed in order to reduction of lignin content in the hope of reducing the pollution of pulping and improving digestibility of forage. Methods to reduce lignin production have focused on altering the path by which lignin is formed. However, these approaches have only served to alter the composition and not the amount of lignin. The review has shown that alternate enzymatic pathways are involved and that plants in which this alternate pathway is blocked produce less lignin. The current review points out the complicated route the leads to lignification and suggests other avenues of research that may lead the ling-sought after goals of reduction of lignin content in wood in the hope of reducing pollutants generated from pulping and increasing forage digestibility.

Technical Abstract: Lignin, a complex phenylpropanoid compound, is polymerized from the monolignols p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol. These three monolignols differ only by the 3- and 5-methoxyl groups. Therefore, enzymatic reactions controlling methoxylations of 3- and 5-positions of monolignol precursors are critical to determine the lignin composition. Recent biochemical and transgenic studies have indicated tha the methylation pathways in monolignol biosynthesis are much more complicated than we have previously envisioned. It has been demonstrated that caffeoyl CoA O-methyltransferase plays a predominant role in the synthesis of guaiacyl lignin unit as well as in the supply of substrates for the synthesis of syringyl lignin unit. Caffeic acid O-methyltransferase has been found to essentially control the biosynthesis of syringyl lignin unit. These new findings have greatly enriched our knowledge on the methylation pathways in monolignol biosynthesis.