Genetic Augmentation of Syringyl Lignin in Low-lignin Aspen Trees, 2004 Paper Summit, Spring Technical & International Environmental Conference, (including Papermakers; Process Control, Electrical & Information; Product & Product Quality)

As a polysaccharide-encrusting component, lignin is critical to cell wall integrity and plant growth but lignin also hinders recovery of cellulose fibers during the wood pulping process. To improve pulping efficiency, it is highly desirable to genetically modify lignin content and/or structure in pulpwood species to maximize pulp yields with minimal energy consumption and environmental impact. Transgenic aspen trees with reduced lignin content have already been produced by antisense down-regulation of a 4-coumarate: coenzyme A ligase (4CL1) gene. The objective of this study was to genetically augment syringyl lignin biosynthesis in the low-lignin trees in order to enhance lignin reactivity during chemical pulping. To accomplish this, both aspen and sweetgum genes encoding coniferaldehyde 5-hydroxylase (CAld5H) were targeted for over-expression in wildtype or low-lignin trees under control of either a constitutive or a xylem-specific promoter. Through the use of Pyrolysis Molecular Beam Mass Spectrometry (pyMBMS) for rapid wood chemical analysis, we observed increased syringyl-to-guaiacyl lignin ratios in the transgenic wood samples, regardless of the promoter used or gene origin. Our results confirmed that the CAld5H gene is key to syringyl lignin biosynthesis. The outcomes of this research should be readily applicable to other pulpwood species, and promise to bring direct economic and environmental benefits to the pulp and paper industry.