Lignin genetic engineering:: Evaluation of lignin alterations and pulping performances of transgenic poplar trees with down-regulated O-methyltransferase and cinnamyl alcohol dehydrogenase

Two-year old poplars with down-regulated caffeic acid O-methyltransferase (COMT) or cinnamyl alcohol dehydrogenase (CAD) were evaluated for lignin structure and kraft pulping. Both lines show similar growth and lignin level as control. While depressed CAD activity does not change the proportion of beta-O-4 bonds and syringyl units, it increases the frequency of free phenolic lignin units, an essential trait for kraft cook. COMT down-regulation severely affects lignin which has less beta-O-4 bonds and S units, but twice more biphenyl bonds than control. Kraft cook is facilitated for CAD transformed line, while more difficult for COMT transformants. This study points the way to genetically mold lignin structure for more easily processed trees.