Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2002
Publication Date: N/A
Citation: Interpretive Summary: There is an enzyme used by all plants in the last step for production of monolignols, the building blocks from which the polymer lignin is produced. (It is lignin that holds fibers together in woody and forage plants; lignin is essential for the plant, but is a limit to plant cell wall digestibility by ruminant animals and an impediment in industrial pulping to make paper. Consequently there is a lot of effort directed toward selection and genetic methods for altering lignins). Some plants are naturally deficient in this enzyme, CAD, and genetic engineers have also recently been able to manipulate the level of the enzyme by regulation of the gene. However, whereas the enzyme levels and gene expression can be measured, the degree of effect on the plant's biochemistry has been difficult to ascertain, except by very detailed and laborious methods. Here we report on the discovery by our French collaborators at INRA of a "molecular marker compound" for CAD, and our work elucidating the structure of the marker. We also deduced that it was derived from diagnostic structures in the lignin arising from incorporation of the aldehyde monolignol precursors. The availability of the marker allows researchers to rapidly assess the effect of CAD levels on plant lignin composition, and therefore provides a more streamlined tool for research aimed at improving plant cell wall utilization.
Technical Abstract: Molecular marker compounds, derived from lignin by the thioacidolysis degradative method, for CAD-deficiency in angiosperms have been structurally identified as indene derivatives. They are shown to derive from hydroxycinnamyl aldehydes that have undergone 8-O-4-cross-coupling during lignification. As such, they are valuable markers for ascertaining plant responses to various levels of CAD-down-regulation. Their derivation illustrates that hydroxycinnamyl aldehydes incorporate into angiosperm lignins by endwise coupling reactions in much the same way as normal monolignols do, suggesting that the hydroxycinnamyl aldehydes should be considered authentic lignin precursors.