Lignification in Transgenic Poplars with Extremely Reduced Caffeic Acid O-Methyltransferase Activity

• Published in: Plant physiology (Bethesda) 2000-08, Vol.123 (4), p.1363-1373
• Main Authors: Lise Jouanin, Thomas Goujon, Véronique de Nadaï, Marie-Thérèse Martin, Isabelle Mila, Christelle Vallet, Pollet, Brigitte, Arata Yoshinaga, Chabbert, Brigitte, Michel Petit-Conil, Lapierre, Catherine
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biochemical Processes and Macromolecular Structures; Biological and medical sciences; caffeic acid O-methyltransferase; Cauliflower mosaic virus; Cellulose - metabolism; Colors; Data lines; Dimers; Fundamental and applied biological sciences. Psychology; Genetics and breeding of economic plants; Lignification; Lignin; Lignin - biosynthesis; Lignin - chemistry; Lignin - metabolism; Metabolism; Metabolism. Physicochemical requirements; Methyltransferases - genetics; Methyltransferases - metabolism; Monomers; Phenotype; Plant physiology and development; Plants; Plants, Genetically Modified - anatomy & histology; Plants, Genetically Modified - genetics; Plants, Genetically Modified - metabolism; Populus alba; Populus tremula; Pulping; Transgenic plants; Trees - anatomy & histology; Trees - genetics; Trees - metabolism; Varietal selection. Specialized plant breeding, plant breeding aims; Wood; Xylem; Yield, quality, earliness, varia
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.123.4.1363

Transgenic poplars (Populus tremula × Populus alba) were obtained by introduction of a sense homologous transgene encoding caffeic acid O-methyltransferase (COMT) under the control either of the cauliflower mosaic virus double 35S promoter or of the eucalyptus cinnamyl alcohol dehydrogenase promoter. Although these constructs conferred a moderate overexpression of COMT in some lines, a transgenic line with the double 35S promoter was found where COMT activity in woody tissues was close to zero due to a gene-silencing phenomenon. For the first time in COMT down-regulated trees, this alteration substantially reduced lignin level in 6-month-old trees (17% decrease). Lignin structure was found to be strongly altered, with a two times higher content in condensed bonds, an almost complete lack of syringyl units, and the incorporation of 5-hydroxyguaiacyl units to the most remarkable extent reported so far. Consistent with the higher cellulose content and with the higher condensation degree of the lignin, the impact of the transformation on the kraft-pulping performances of the poplar trees positively affected the pulp yield (10% relative increase), but made lignins less amenable to industrial degradations.