Wagner Armin, Tobimatsu Yuki, Phillips Lorelle, Flint Heather, Geddes Barbara, Lu Fachuang, Ralph John
Biotransformation Department, Scion, 3020, Rotorua 3010, New Zealand;
Department of Biochemistry, University of Wisconsin, Madison, WI 53706; and US Department of Energy's Great Lakes Bioenergy Research Center, The Wisconsin Energy Institute, Madison, WI 53726.
Proc Natl Acad Sci U S A. 2015 May 12;112(19):6218-23. doi: 10.1073/pnas.1411926112. Epub 2015 Apr 20.
Conifers (softwoods) naturally lack syringyl units in their lignins, rendering lignocellulosic materials from such species more difficult to process than syringyl-rich hardwood species. Using a transformable Pinus radiata tracheary element (TE) system as an experimental platform, we investigated whether metabolic engineering can be used to create syringyl lignin in conifers. Pyrolysis-GC/MS and 2D-NMR analysis of P. radiata TE cultures transformed to express ferulate 5-hydroxylase (F5H) and caffeic acid O-methyltransferase (COMT) from Liquidambar styraciflua confirmed the production and incorporation of sinapyl alcohol into the lignin polymer. Transformation with F5H was sufficient for the production of syringyl lignin in TEs, but cotransformation with COMT improved its formation. In addition, lower levels of the pathway intermediate 5-hydroxyconiferyl alcohol were evidenced in cotransformation experiments, indicating that the introduction of the COMT overcame the inefficiency of the native pine methyltransferases for supporting sinapyl alcohol production.Our results provide the proof of concept that it is possible to generate a lignin polymer that contains syringyl units in softwood species such as P. radiata, suggesting that it might be possible to retain the outstanding fiber properties of softwoods while imbuing them with the lignin characteristics of hardwoods that are more favorable for industrial processing.
针叶树（软木）的木质素天然缺乏紫丁香基单元，这使得此类树种的木质纤维素材料比富含紫丁香基的阔叶树种的材料更难加工。我们以可转化的辐射松管状分子（TE）系统作为实验平台，研究了代谢工程是否可用于在针叶树中生成紫丁香基木质素。对转化后表达来自胶皮枫香树的阿魏酸5 - 羟化酶（F5H）和咖啡酸O - 甲基转移酶（COMT）的辐射松TE培养物进行热解 - 气相色谱/质谱分析和二维核磁共振分析，证实了芥子醇生成并掺入到木质素聚合物中。用F5H转化足以在TE中产生紫丁香基木质素，但与COMT共转化可改善其形成。此外，在共转化实验中发现途径中间体5 - 羟基松柏醇的水平较低，这表明COMT的引入克服了天然松树甲基转移酶在支持芥子醇生成方面的低效性。我们的结果提供了概念验证，即有可能在辐射松等软木树种中生成含有紫丁香基单元的木质素聚合物，这表明在保留软木优异纤维性能的同时，赋予它们更有利于工业加工的阔叶树木质素特性或许是可行的。
