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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

The Effects on Lignin Structure of Overexpression of Ferulate 5-Hydroxylase in Hybrid Poplar^1[W]

Department of Wood Science, University of British Columbia, Vancouver, Canada V6T 1Z4 (J.J.S., S.D.M.); Department of Biochemistry and Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, Wisconsin 53706 (T.A., J.R.); and Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907 (C.C.)

Poplar (Populus tremula x alba) lignins with exceedingly high syringyl monomer levels are produced by overexpression of the ferulate 5-hydroxylase (F5H) gene driven by a cinnamate 4-hydroxylase (C4H) promoter. Compositional data derived from both standard degradative methods and NMR analyses of the entire lignin component (as well as isolated lignin fraction) indicated that the C4H::F5H transgenic's lignin was comprised of as much as 97.5% syringyl units (derived from sinapyl alcohol), the remainder being guaiacyl units (derived from coniferyl alcohol); the syringyl level in the wild-type control was 68%. The resultant transgenic lignins are more linear and display a lower degree of polymerization. Although the crucial β-ether content is similar, the distribution of other interunit linkages in the lignin polymer is markedly different, with higher resinol (β-β) and spirodienone (β-1) contents, but with virtually no phenylcoumarans (β-5, which can only be formed from guaiacyl units). p-Hydroxybenzoates, acylating the -positions of lignin side chains, were reduced by >50%, suggesting consequent impacts on related pathways. A model depicting the putative structure of the transgenic lignin resulting from the overexpression of F5H is presented. The altered structural features in the transgenic lignin polymer, as revealed here, support the contention that there are significant opportunities to improve biomass utilization by exploiting the malleability of plant lignification processes.

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.109.137059

^* Corresponding author; e-mail shawnman{at}interchange.ubc.ca.

Received February 17, 2009; accepted April 20, 2009; published April 22, 2009.