Ghent University, Department of Plant Biotechnology and Bioinformatics, 9052 Ghent, Belgium.
VIB Center for Plant Systems Biology, 9052 Ghent, Belgium.
Plant Physiol. 2017 Nov;175(3):1018-1039. doi: 10.1104/pp.17.00834. Epub 2017 Sep 6.
In the search for renewable energy sources, genetic engineering is a promising strategy to improve plant cell wall composition for biofuel and bioproducts generation. Lignin is a major factor determining saccharification efficiency and, therefore, is a prime target to engineer. Here, lignin content and composition were modified in poplar ( × ) by specifically down-regulating () by a hairpin-RNA-mediated silencing approach, which resulted in only 5% residual transcript abundance. These transgenic lines showed no biomass penalty despite a 10% reduction in Klason lignin content and severe shifts in lignin composition. Nuclear magnetic resonance spectroscopy and thioacidolysis revealed a strong increase (up to 20-fold) in sinapaldehyde incorporation into lignin, whereas coniferaldehyde was not increased markedly. Accordingly, ultra-high-performance liquid chromatography-mass spectrometry-based phenolic profiling revealed a more than 24,000-fold accumulation of a newly identified compound made from 8-8 coupling of two sinapaldehyde radicals. However, no additional cinnamaldehyde coupling products could be detected in the CAD1-deficient poplars. Instead, the transgenic lines accumulated a range of hydroxycinnamate-derived metabolites, of which the most prominent accumulation (over 8,500-fold) was observed for a compound that was identified by purification and nuclear magnetic resonance as syringyl lactic acid hexoside. Our data suggest that, upon down-regulation of , coniferaldehyde is converted into ferulic acid and derivatives, whereas sinapaldehyde is either oxidatively coupled into S'(8-8)S' and lignin or converted to sinapic acid and derivatives. The most prominent sink of the increased flux to hydroxycinnamates is syringyl lactic acid hexoside. Furthermore, low-extent saccharification assays, under different pretreatment conditions, showed strongly increased glucose (up to +81%) and xylose (up to +153%) release, suggesting that down-regulating is a promising strategy for improving lignocellulosic biomass for the sugar platform industry.
在寻找可再生能源的过程中，基因工程是一种很有前途的策略，可以改善植物细胞壁的组成，从而生成生物燃料和生物制品。木质素是决定糖化效率的主要因素，因此是工程改造的主要目标。在这里，通过发夹 RNA 介导的沉默方法特异性下调杨树（ × ）中的 （），从而改变木质素的含量和组成，使 （）的转录本丰度仅残留 5%。尽管克氏木质素含量降低了 10%，木质素组成发生了严重变化，但这些转基因品系并没有出现生物量损失。核磁共振波谱和硫代酸解表明，木质素中丁香醛的掺入量大幅增加（高达 20 倍），而松柏醛则没有明显增加。相应地，基于超高效液相色谱-质谱的酚类分析显示，一种新鉴定的化合物的积累超过了 24,000 倍，该化合物由两个丁香醛自由基的 8-8 偶联形成。然而，在 CAD1 缺陷型杨树上未能检测到其他肉桂醛偶联产物。相反，转基因品系积累了一系列羟基肉桂酸衍生代谢物，其中最显著的积累（超过 8,500 倍）是一种通过纯化和核磁共振鉴定为丁香基乳酸己糖苷的化合物。我们的数据表明，下调 后，松柏醛转化为阿魏酸和衍生物，而丁香醛要么被氧化偶联成 S'（8-8）S'和木质素，要么转化为丁香酸和衍生物。增加的羟基肉桂酸通量的主要汇点是丁香基乳酸己糖苷。此外，在不同预处理条件下进行的低程度糖化测定表明，葡萄糖（高达 +81%）和木糖（高达 +153%）的释放量显著增加，这表明下调 是提高木质纤维素生物质用于糖平台工业的有前途的策略。
