Zhong Ruiqin, Morrison W Herbert, Negrel Jonathan, Ye Zheng-Hua
Department of Botany, University of Georgia, Athens, Georgia 30602, USA.
Plant Cell. 1998 Dec;10(12):2033-46. doi: 10.1105/tpc.10.12.2033.
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.
咖啡酰辅酶A（CoA）O-甲基转移酶（CCoAOMT）被认为参与木质素生物合成的另一条甲基化途径。然而，尚无直接证据证实CCoAOMT对木质素生物合成至关重要。为了进一步了解木质素生物合成中的甲基化步骤，我们采用反义方法改变O-甲基转移酶（OMT）基因表达，并研究这种改变的后果。我们培育出了CCoAOMT大幅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，仅CCoAOMT的降低就导致木质素含量大幅下降。CCoAOMT的降低还导致木质素组成发生显著变化。转基因植株中的愈创木基木质素和紫丁香基木质素均减少。然而，愈创木基木质素优先减少，导致S/G（紫丁香基/愈创木基）比值增加。我们还分析了CCoAOMT和CAOMT同时降低的转基因植株中的木质素含量和组成。两种OMT的降低导致总木质素含量进一步下降。这与仅CAOMT降低所产生的效果形成鲜明对比，后者仅降低了紫丁香基木质素单元，而总木质素含量并未降低。这些结果明确表明，木质素生物合成中的甲基化反应由CCoAOMT和CAOMT共同催化。
