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Title: ESSENTIAL ROLE OF CAFFEOYL COA O-METHYLTRANSFERASE IN LIGNIN BIOSYNTHESIS IN WOODY POPLAR PLANTS

Author
item ZHONG, RUIQIN - UNIVERSITY OF GEORGIA
item MORRISON III, WILEY
item HIMMELSBACH, DAVID
item POOLE, FARRIS
item YE, ZHENG-HUA - UNIVERSITY OF GEORGIA

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/12/2000
Publication Date: 10/15/2000
Citation: Zhong, R., Morrison III, W.H., Himmelsbach, D.S., Poole, F.L., Ye, Z. 2000. Essential role of caffeoyl coa o-methyltransferase in lignin biosynthesis in woody poplar plants. Plant Physiology. Vol. 124, pp. 563-577.

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 research has been the 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 current work has shown that an alternate enzymatic pathway is involved and that plants in which this alternate pathway has been blocked produce less lignin. Earlier work has demonstrated that lignin composition and content has been reduced in transgenic tobacco plants. The current work demonstrated this same affect on woody plants and represents another step toward 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: Caffeoyl CoA O-methyltransferase (CCoAOMT) has recently been shown to participate in lignin biosynthesis in herbacious tobacco plants. Here, we demonstrate that CCoAOMT is essential in lignin biosynthesis in woody poplar plants. In poplar stems, CCoAOMT was found to be expressed in all lignifying cells including vessel elements and fibers as well as in xylem ray parenchyma cells. Repression of CCoAOMT expression by the antisense approach in transgenic poplar plants caused a significant decrease in total lignin content as detected by both Klason lignin assay and Fourier- transform infrared spectroscopy. The reduction in lignin content was the result of a decrease in both guaiacyl and syringyl lignins as determined by in-source pyrolysis mass spectroscopy. Fourier-transform infrared spectroscopy indicated that the reduction in lignin content resulted in a less condensed and less cross-linked lignin structure in wood. Repression of CCoAOMT expression also led to coloration of wood and an elevation of wall-bound hydroxybenzoic acid. Taken together, these results indicate that CCoAOMT plays a dominant role in methylation of 3-hydroxyl group of caffeoyl CoA, and the CCoAOMT-mediated methylation reaction is essential to channel substrates for 5 methoxylation of hydroxycinnamates. They also suggest that antisense repression of CCoAOMT is an efficient means for genetic engineering of trees with low lignin content.