Genetic engineering of poplar lignins: impact of lignin alteration on Kraft pulping performances

A poplar clone (INRA 717-1B4) was genetically engineered to downregulate caffeic acid O-methyltransferase (COMT) or/and cinnamyl alcohol dehydrogenase (CAD), which are enzymes of the lignin biosynthetic pathway. One- and two-year old transgenic poplars with severely down-regulated COMT or CAD activity were evaluated for lignin structure and for kraft pulping characteristics. While the subtle lignin alterations caused by CAD depressed activity had a beneficial impact on pulping efficiency, the structural changes induced by COMT down-regulation detrimentally affected the kraft delignification of the poplar trees. These phenomena could be rationally accounted for by the observed alteration of lignin structure. These results point the way to change lignin structure by genetic engineering in order to produce more easily processed trees for the pulp industries