Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 2/17/2002
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: How do plants respond when genetic engineers knock out genes for enzymes that are (supposedly) required to produce crucial cell wall polymers, such as lignin? Lignins are one of the worlds most abundant natural polymers that are unusual because, while formed from relatively few simple components, they are assembled in somewhat combinatorial fashion. As such, there are probably no two lignin polymers over a certain (unspecified) size that are structurally identical. They are therefore not amenable to all the wonderful techniques that are used for ¿NMR-designed¿ polymers such as proteins! Nevertheless, NMR provides the most powerful insights into the structures of these complex polymers, and has become the preeminent way of revealing just how the plant chemistry/biochemistry is affected when genes are up- or down-regulated. The techniques are not novel ¿ pretty standard (gradient enhanced) HMQC/HSQC, HMQC-TOCSY, HMBC methods (although we have recently made good use of Bruker¿s cryoprobe technology), but the spectra are neat, revealing, and the implications are quite stunning. Manipulating specific lignin-biosynthetic-pathway genes, such as one producing the pathway methylation enzyme ¿COMT¿, produces profound alterations in lignins, apparently realized by a plant¿s (controversial) ability to incorporate other components at its disposal when unable to make its traditional monomers. In the case of COMT-deficiency, the plant incorporates significant quantities of 5-hydroxyconiferyl alcohol, the immediate precursor of sinapyl alcohol (a traditional lignin monomer), into its lignin. As a result, novel benzodioxane structures become dominant structures in the polymer, as beautifully revealed by 2D and 3D NMR. The recognition that normally minor or novel units can incorporate into lignins provides significantly expanded opportunities for engineering their composition and consequent properties to improve processes ranging from digestibility in ruminant animals to chemical pulping for paper production.