A novel lignin in poplar trees with a reduced caffeic acid/5-hydroxyferulic acid O-methyltransferase activity
Lignin is a polymeric constituent of the cell wall that needs to be removed during the paper making process. Bi-specific caffeic acid/5-hydroxyferulic acid O-methyltransferase (COMT) catalyses the O-methylation of caffeic acid and 5-hydroxyferulic acid to ferulic acid and sinapic acid, respectively. These compounds are intermediates in the biosynthesis of the lignin precursors. Therefore, COMTs are potential target enzymes for reducing the amount, or modifying the composition, of lignin in plants. Different antisense and sense constructs have been expressed of a gene encoding a COMT from poplar (Populus trichocarpa x P. deltoides) in a P. tremula x P. alba clone under the control of the cauliflower mosaic virus 35S promoter. From all analysed transformants, four lines transformed with an antisense construct had a reduced COMT activity. Two showed a 50% reduction of COMT activity, which altered only slightly the monomeric composition. In the two other transformants, the COMT activity was reduced by 95%. In the latter case, the syringyl/ guaiacyl ratio (S/G) was reduced by sixfold (due to a decrease of S and an increase of G), as analysed by thioacidolysis. A new component of lignin, the 5-hydroxyguaiacyl residue, was detected among the thioacidolysis products. Moreover, in contrast to the white/yellow colour of wild-type wood, the xylem of the transgenic lines with a 95% reduction of COMT activity was pale rose. A similar phenotype was observed in brown-midrib mutants of maize and sorghum, known for their altered lignification. Although the lignin composition was consistently modified, the lignin content of the transgenic poplars was similar to that of the controls.
Document Type: Research Article
Affiliations: 1: Laboratorium voor Genetica, Universiteit Gent, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium 2: Laboratoire de Biologie Cellulaire, Institut National de la Recherche Agronomique, F-78026, Versailles Cedex, France 3: Laboratoire de Chimie Biologique, Institut National de la Recherche Agronomique, F-78850 Thiverval-Grignon, France 4: Centre Technique du Papier, F-38044 Grenoble Cedex, France 5: Station d'Amélioration des Arbres Forestiers, Institut National de la Recherche Agronomique, F-45160 Ardon, France 6: Laboratoire Associé de l'Institut National de la Recherche Agronomique, Universiteit Gent, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium
Publication date: December 1, 1995