Cuiying Chen

Biotechnology in trees: towards improved paper pulping by lignin engineering

Lignin is a heterogenous phenolic polymer that plays crucial roles in the development and physiology of vascular plants. However, it needs to be removed from cellulose by toxic and energy-requiring processes for the production of high-quality paper. Therefore, a major biotechnological challenge is to obtain transgenic trees with modified lignin to improve the quality of wood for paper making. Here, we review the results obtained by alterating the expression of genes of the monolignol biosynthesis pathway in trees and the effect of these modifications on the lignin polymer and on pulping. The data reported show that lignin engineering is a promising strategy to improve wood quality for the pulp and paper industry.

Applications of molecular genetics for biosynthesis of novel lignins

Abstract 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 down-regulation of COMT. Transgenic poplars with a reduced CAD activity have better pulping properties, due to a higher extractability of the lignin.

Lignin Biosynthesis in Poplar: Genetic Engineering and Effects on Kraft Pulping

ABSTRACT Transgenic poplar, downregulated in cinnamyl alcohol dehydrogenase (CAD) or caffeic acid-O-methyltransferase (COMT) expression have been grown in field trials. Wood of these trees has been evaluated for Kraft pulping. The results show that lignin is more easily extracted from wood of the CAD-downregulated trees, whereas wood from COMT-downregulated trees is less suitable for Kraft pulping. Detailed NMR analyses of lignin from COMT-downregulated poplars reveal the presence of benzodioxane structures, which are derived from coupling of 5-hydroxyconiferyl alcohol with the lignin polymer, showing that monolignols other than p-coumaryl, coniferyl and sinapyl alcohol can be incorporated into lignin. Analysis of poplar downregulated for CCoAOMT shows that CCoAOMT is involved in the synthesis of both syringyl and guaiacyl units, and that sinapic is probably not an important precursor for syringyl lignin synthesis.