NMR characterization of lignins from transgenic poplars with suppressed caffeic acid O-methyltransferase activity

Abstract

Perturbing the lignin biosynthetic pathway provides a tool for understanding the complex process of lignification. Caffeic acid O-methyltransferase (COMT) is required to produce syringyl units in lignins. Down-regulating the expression of its gene in poplar dramatically affects the lignin composition. 2D and 3D NMR investigations detail structural differences between lignins from a control and COMT-deficient poplars obtained by means of two independent transformation techniques. This first application of 3D NMR to natural abundance lignins reveals the full side-chain network and provides diagnostic evidence for the intimate incorporation of 5-hydroxyconiferyl alcohol into the lignins to form novel benzodioxanes as major structures. The flexibility of a plant to utilize novel monomers to produce functional lignins provides opportunities for engineering the structure and affecting the consequent properties of lignins.