Dual Methylation Pathways in Lignin Biosynthesis
Dual Methylation Pathways in Lignin Biosynthesis
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DOI：
10.1105/tpc.10.12.2033
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发表时间：
1998-12
期刊：
影响因子：
11.6
通讯作者：
R. Zhong;W. Herbert;Morrison Iii;J. Negrel;Z. Ye
中科院分区：
文献类型：
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作者：
R. Zhong;W. Herbert;Morrison Iii;J. Negrel;Z. Ye
咖啡酰基辅酶A (CoA) o -甲基转移酶（CCoAOMT）被认为参与木质素生物合成的另一种甲基化途径。然而，没有直接证据证实CCoAOMT是木质素生物合成所必需的。为了进一步了解木质素生物合成中的甲基化步骤，我们使用反义方法改变o -甲基转移酶（OMT）基因表达，并研究了这种改变的后果。我们获得了CCoAOMT显著降低的转基因烟草植株，以及CCoAOMT和咖啡酸o -甲基转移酶（CAOMT）同时降低的植株。木质素分析表明，单独降低CCoAOMT可显著降低木质素含量。CCoAOMT的减少也导致木质素组成的显著变化。愈创木酰木质素和丁香酰木质素在转基因植株中均减少。而愈创木酰基木质素优先减少，导致S/G（丁香/愈创木酰基）比升高。我们还分析了CCoAOMT和CAOMT同时降低的转基因植物的木质素含量和组成。两种OMTs的减少导致总木质素含量进一步降低。这与单独减少CAOMT所产生的效果形成鲜明对比，CAOMT只降低了注射器木质素单位，而没有降低总体木质素含量。这些结果明确表明，木质素生物合成中的甲基化反应是由CCoAOMT和CAOMT催化的。
Caffeoyl–coenzyme A (CoA) O-methyltransferase (CCoAOMT) has been proposed to be involved in an alternative methylation pathway of lignin biosynthesis. However, no direct evidence has been available to confirm that CCoAOMT is essential for lignin biosynthesis. To understand further the methylation steps in lignin biosynthesis, we used an antisense approach to alter O-methyltransferase (OMT) gene expression and investigated the consequences of this alteration. We generated transgenic tobacco plants with a substantial reduction in CCoAOMT as well as plants with a simultaneous reduction in both CCoAOMT and caffeic acid O-methyltransferase (CAOMT). Lignin analysis showed that the reduction in CCoAOMT alone resulted in a dramatic decrease in lignin content. The reduction in CCoAOMT also led to a dramatic alteration in lignin composition. Both guaiacyl lignin and syringyl lignin were reduced in the transgenic plants. However, guaiacyl lignin was preferentially reduced, which resulted in an increase in the S/G (syringl/guaiacyl) ratio. We have also analyzed lignin content and composition in transgenic plants having a simultaneous reduction in both CCoAOMT and CAOMT. The reduction in both OMTs resulted in a further decrease in total lignin content. This is in sharp contrast to the effect that resulted from the reduction in CAOMT alone, which only decreased the syringl lignin unit without a reduction in overall lignin content. These results unequivocally demonstrate that methylation reactions in lignin biosynthesis are catalyzed by both CCoAOMT and CAOMT.