Department of Plant Systems Biology, VIB, 9052 Gent, Belgium.
Plant J. 2010 Dec;64(6):885-97. doi: 10.1111/j.1365-313X.2010.04353.x. Epub 2010 Oct 15.
Lignin engineering is a promising strategy to optimize lignocellulosic plant biomass for use as a renewable feedstock for agro-industrial applications. Current efforts focus on engineering lignin with monomers that are not normally incorporated into wild-type lignins. Here we describe an Arabidopsis line in which the lignin is derived to a major extent from a non-traditional monomer. The combination of mutation in the gene encoding caffeic acid O-methyltransferase (comt) with over-expression of ferulate 5-hydroxylase under the control of the cinnamate 4-hydroxylase promoter (C4H:F5H1) resulted in plants with a unique lignin comprising almost 92% benzodioxane units. In addition to biosynthesis of this particular lignin, the comt C4H:F5H1 plants revealed massive shifts in phenolic metabolism compared to the wild type. The structures of 38 metabolites that accumulated in comt C4H:F51 plants were resolved by mass spectral analyses, and were shown to derive from 5-hydroxy-substituted phenylpropanoids. These metabolites probably originate from passive metabolism via existing biochemical routes normally used for 5-methoxylated and 5-unsubstituted phenylpropanoids and from active detoxification by hexosylation. Transcripts of the phenylpropanoid biosynthesis pathway were highly up-regulated in comt C4H:F5H1 plants, indicating feedback regulation within the pathway. To investigate the role of flavonoids in the abnormal growth of comt C4H:F5H1 plants, a mutation in a gene encoding chalcone synthase (chs) was crossed in. The resulting comt C4H:F5H1 chs plants showed partial restoration of growth. However, a causal connection between flavonoid deficiency and this restoration of growth was not demonstrated; instead, genetic interactions between phenylpropanoid and flavonoid biosynthesis could explain the partial restoration. These genetic interactions must be taken into account in future cell-wall engineering strategies.
木质素工程是一种很有前途的策略，可以优化木质纤维素植物生物质，将其作为可再生原料用于农业工业应用。目前的研究重点是用通常不掺入野生型木质素的单体来工程木质素。在这里，我们描述了一种拟南芥品系，其木质素主要来源于一种非传统单体。在 caffeic 酸 O-甲基转移酶（comt）基因的突变与香豆酸 4-羟化酶启动子（C4H：F5H1）下过量表达阿魏酸 5-羟化酶的组合，导致植物具有独特的木质素，几乎 92%由苯并二恶烷单元组成。除了这种特殊木质素的生物合成外，与野生型相比，comt C4H：F5H1 植物的酚类代谢发生了巨大变化。通过质谱分析解析了在 comt C4H：F51 植物中积累的 38 种代谢物的结构，它们来自 5-羟基取代的苯基丙醇类。这些代谢物可能源自通过现有生化途径的被动代谢，这些途径通常用于 5-甲氧基化和 5-未取代的苯基丙醇类，以及通过己糖基化的主动解毒。comt C4H：F5H1 植物中苯丙烷生物合成途径的转录本高度上调，表明途径内存在反馈调节。为了研究类黄酮在 comt C4H：F5H1 植物异常生长中的作用，将 chalcone synthase（chs）基因的突变与 comt C4H：F5H1 进行了杂交。所得的 comt C4H：F5H1 chs 植物显示出部分生长恢复。然而，并未证明类黄酮缺乏与这种生长恢复之间存在因果关系；相反，类黄酮生物合成与苯丙烷生物合成之间的遗传相互作用可以解释这种部分恢复。在未来的细胞壁工程策略中必须考虑到这些遗传相互作用。
