Transgenic Poplar Trees with Altered Lignin and Improved Pulping Characteristics, 1997 Biological Sciences Symposium Proceedings

A poplar hybrid clone (P. tremula x P. alba, INRA 717-lB4) has been genetically engineered with genes encoding key enzymes from the lignin biosynthetic pathway [l] [2]. Caffeic acid O-methyltransferase (COMT), and cinnamyl alcohol dehydrogenase (CAD) activities have been followed during the growing season in wild-type trees and in trees down-regulated for either CAD or OMT activity. Two peaks of activity are detected for both enzymes in the wild-type trees. In contrast, antisense or cosuppression plants generally showed reduced levels of COMT and CAD activities, even though apparent seasonal variations were observed.

In trees older than 5 months, a significant reduction in lignin content is observed in two transgenic lines with low CAD activity, and the lignin is notably enriched in free phenolic groups and in diarylpropane 13-l bonds: these modifications probably account for the easier delignil1cation of 2-year-old CAD transgenic trees.

Poplars with low COMT activity show a high content in G units, and in carbon-carbon bonds, together with an increase in the relative abundance of biphenyl and phenylcoumaran dimers in the lignin polymer: these changes probably contribute to the poor performance of this material for kraft pulping.

Preliminary lignin analyses have been performed on double transgenic poplar trees altered for both COMT and CAD activities.