Genes Involved in the Final Steps of Monolignol Biosynthesis and Their Manipulation for Tailoring New Lignins

The genes encoding cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) have been cloned and characterized in Eucalyptus gunnii . Their spatio-temporal expression has been investigated with a combination of techniques revealing a high level of expression associated with lignifying tissues. CCR down-regulated tobacco plants have been obtained and exhibit an unusual yellow-brown coloration of the xylem. Chemical and ultrastructural modifications including a decrease in lignin content were observed. CAD down-regulated transgenic tobacco plants have also been obtained through the use of different antisense constructs. Several chemical modifications are induced in transgenic lignins which exhibit an increased extractability, a positive attribute for the pulping industry. The results presented here confirm that lignin content and composition can be modified by directed genetic manipulation of genes specifically involved in monolignol biosynthesis.