BioEnergy Research

, Volume 5, Issue 4, pp 1009-1019

First online:

Open Access This content is freely available online to anyone, anywhere at any time.

Effects on Lignin Structure of Coumarate 3-Hydroxylase Downregulation in Poplar

  • John RalphAffiliated withDepartment of Biochemistry, Enzyme Institute, University of Wisconsin-MadisonDepartment of Biological Systems Engineering, University of Wisconsin-MadisonDOE Great Lakes Bioenergy Research Center, and Wisconsin Bioenergy Initiative, University of Wisconsin-Madison Email author 
  • , Takuya AkiyamaAffiliated withWood Chemistry Laboratory, Department of Biomaterial Sciences, the University of Tokyo
  • , Heather D. ColemanAffiliated withDepartment of Biology, Syracuse University
  • , Shawn D. MansfieldAffiliated withDepartment of Wood Science, University of British Columbia


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 lignin p-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.


Gene downregulation NMR Thioacidolysis Digestibility Biomass conversion Lignin composition