Genetic Augmentation of Syringyl Lignin in Low-lignin Aspen Trees

摘要

As a polysaccharide-encrusting component, lignin is critical to cell wall integrity and plant growth but lignin alsornhinders recovery of cellulose fibers during the wood pulping process. To improve pulping efficiency, it is highlyrndesirable to genetically modify lignin content and/or structure in pulpwood species to maximize pulp yields withrnminimal energy consumption and environmental impact. Transgenic aspen trees with reduced lignin content havernalready been produced by antisense down-regulation of a 4-coumarate: coenzyme A ligase (4CL1) gene. Thernobjective of this study was to genetically augment syringyl lignin biosynthesis in the low-lignin trees in order tornenhance lignin reactivity during chemical pulping. To accomplish this, both aspen and sweetgum genes encodingrnconiferaldehyde 5-hydroxylase (CAld5H) were targeted for over-expression in wildtype or low-lignin trees underrncontrol of either a constitutive or a xylem-specific promoter. Through the use of Pyrolysis Molecular Beam MassrnSpectrometry (pyMBMS) for rapid wood chemical analysis, we observed increased syringyl-to-guaiacyl lignin ratiosrnin the transgenic wood samples, regardless of the promoter used or gene origin. Our results confirmed that thernCAld5H gene is key to syringyl lignin biosynthesis. The outcomes of this research should be readily applicable tornother pulpwood species, and promise to bring direct economic and environmental benefits to the pulp and paperrnindustry.