Manipulation of lignin composition in transgenic poplar trees by antisense strategy

*INRA, Station d'Amélioration des Arbres Forestiers, Orléans Diffusion du document : INRA, Station d'Amélioration des Arbres Forestiers, Orléans

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Inglés. Lignin is a major waste product of paper pulp production and its removal requires energy demanding and highly polluting chemical treatments. Both lignin content and composition have an impact on the pulping process. Our interest is to modify, by gene engineering, the lignin composition and/or content. This would have both economic and environmental benefits, through lower pulping cost and less pulp mill waste, respectively. To this end several genes, known to be involved in lignin biosynthesis, have been cloned from poplar. O-Methyltransferase (OMT; EC 2.1.1.6) plays an important role in the synthesis of lignin by catalyzing the O-methylation of the lignin precursors. By introduction of an antisense OMT gene, under the control of the CaMV 35S promoter, we were able to reduce the amount of O-methylation of the lignin precursors, leading to a lower syringyl/guaiacyl ratio. In these plants the OMT activity was reduced up to 50% of the control.The last step in the biosynthesis of the monolignols is catalyzed by cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195.). Expression of an antisense CAD gene in poplar leads to trees with strongly reduced CAD activity (up to 20% of the value of the control). Surprisingly, the reduced enzymatic activity was in most cases correlated with a red coloration of the xylem. Interestingly, a reduction of the kappa number was observed without any degradation of cellulose and fiber structure. The lignin content was not modified.