Hardwood Lignin Engineered into Softwoods
Conifer (softwood) biomass naturally has high lignin content and is more difficult to process than biomass from hardwood species because softwoods lack syringyl units in their lignins. Using genetic engineering strategies, researchers from the Department of Energy’s Great Lakes Bioenergy Research Center transformed into Pinus radiata two enzyme functions necessary to produce syringyl units in order to metabolicly engineer syringyl lignin production into conifers. Analytical methods performed on the transformed P. radiata showed evidence that the new enzymatic activities were being expressed—namely, ferulate 5-hydroxylase (F5H) and caffeic acid O-methyltransferase (COMT)—and that sinapyl alcohol was being incorporated into the lignin polymer. These results provide the proof of concept that generating a lignin polymer containing syringyl units is possible in softwood species such as P. radiata. Additionally, these results suggest that retaining the outstanding fiber properties of softwoods while imbuing them with the lignin characteristics of hardwoods more favorable for industrial processing also may be possible.
Wagner, A., Y. Tobimatsu, L. Phillips, H. Flint, B. Geddes, F. Lu, and J. Ralph. 2015. “Syringyl Lignin Production in Conifers: Proof of Concept in a Pine Tracheary Element System,” Proceedings of the National Academy of Sciences (USA), DOI: 10.1073/pnas.1411926112.