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

Perturbing the lignin biosynthetic pathway provides a tool for understandin g the complex process of lignification. Caffeic acid O-methyltransferase (C OMT) is required to produce syringyl units in lignins. Down-regulating the expression of its gene in poplar dramatically affects the lignin compositio n. 2D and 3D NMR investigations detail structural differences between ligni ns from a control and COMT-deficient poplars obtained by means of two indep endent transformation techniques. This rst application of 3D NMR to natural abundance lignins reveals the full side-chain network and provides diagnos tic evidence for the intimate incorporation of 5-hydroxyconiferyl alcohol i nto the lignins to form novel benzodioxanes as major structures. The flexib ility of a plant to utilize novel monomers to produce functional lignins pr ovides opportunities for engineering the structure and affecting the conseq uent properties of lignins.