Applications of molecular genetics for biosynthesis of novel lignins

For the production of high-quality paper, lignin needs to be removed from cellulose. This process is energy requiring, expensive and toxic. Molecular biology offers tools to generate trees with a modified lignin composition to facilitate the extractability of lignin. We have cloned several genes encoding enzymes in the methylation of the lignin monomers [bi-specific caffeic acid/5-hydroxyferulic acid O-methyltransferase (COMT) and caffeoyl-CoA O-methyltransferase], and encoding enzymes specific for the lignin biosynthesis pathway [cinnamoyl-CoA reductase and cinnamyl alcohol dehydrogenase (CAD)]. The antisense strategy is used to study the effect of a down-regulation of these enzymes on the lignin content and the lignin composition of poplar wood. Our results demonstrate that the monomeric composition of lignin was dramatically affected by downregulation of COMT. Transgenic poplars with a reduced CAD activity have better pulping properties, due to a higher extractability of the lignin. (C) 1998 Elsevier Science Limited. All rights reserved.