title: Effects on Lignin Structure of Coumarate 3-Hydroxylase Downregulation in Poplar.
abstract: The lignin structural ramifications of coumarate 3-hydroxylase (C3H) downregulation have not been addressed in hardwoods. Such information is required to accompany an assessment of the digestibility and bioenergy performance characteristics of poplar, in particular. Structurally rich 2D NMR methods were applied to the entire lignin fraction to delineate ligninp-hydroxyphenyl:guaiacyl:syringyl (H:G:S) levels and linkage distribution changes (and to compare with traditional degradative analyses). C3H downregulation reduced lignin levels by half and markedly increased the proportion of H units relative to the normally dominant G and S units. Relative stem H unit levels were up by ∼ 100-fold to ∼ 31 %, almost totally at the expense of G units; differences in the lignin interunit linkage distributions were more subtle. The H level in the most drastically C3H-downregulated transgenic poplar falls well beyond the H:G:S compositional bounds of normal angiosperms. The response observed here, in poplar, differs markedly from that reported for alfalfa where the S:G ratio remained almost constant even at substantial H levels, highlighting the often differing responses among plant species.
authors.affiliation: Department of Biochemistry, Enzyme Institute, University of Wisconsin-Madison, 1710 University Avenue, Madison, WI 53726 USA ; Department of Biological Systems Engineering, University of Wisconsin-Madison, 460 Henry Mall, Madison, WI 53706 USA ; DOE Great Lakes Bioenergy Research Center, and Wisconsin Bioenergy Initiative, University of Wisconsin-Madison, Madison, WI 53706 USA.
authors.forename: John
authors.initials: J
authors.lastname: Ralph
authors.affiliation: Wood Chemistry Laboratory, Department of Biomaterial Sciences, the University of Tokyo, Bunkyo-ku Tokyo, 113-8657 Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Akiyama
authors.affiliation: Department of Biology, Syracuse University, 460 Life Sciences Complex, 107 College Place, Syracuse, NY 13244 USA.
authors.forename: Heather D
authors.initials: HD
authors.lastname: Coleman
authors.affiliation: Department of Wood Science, University of British Columbia, Vancouver, BC V6T 1Z4 Canada.
authors.forename: Shawn D
authors.initials: SD
authors.lastname: Mansfield
keywords: Biomass conversion; Digestibility; Gene downregulation; Lignin composition; NMR; Thioacidolysis