Guo D, Chen F, Inoue K, Blount J W, Dixon R A
Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73401, USA.
Plant Cell. 2001 Jan;13(1):73-88. doi: 10.1105/tpc.13.1.73.
Transgenic alfalfa plants were generated harboring caffeic acid 3-O-methyltransferase (COMT) and caffeoyl CoA 3-O-methyltransferase (CCOMT) cDNA sequences under control of the bean phenylalanine ammonia-lyase PAL2 promoter. Strong downregulation of COMT resulted in decreased lignin content, a reduction in total guaiacyl (G) lignin units, a near total loss of syringyl (S) units in monomeric and dimeric lignin degradation products, and appearance of low levels of 5-hydroxy guaiacyl units and a novel dimer. No soluble monolignol precursors accumulated. In contrast, strong downregulation of CCOMT led to reduced lignin levels, a reduction in G units without reduction in S units, and increases in beta-5 linked dimers of G units. Accumulation of soluble caffeic acid beta-d-glucoside occurred only in CCOMT downregulated plants. The results suggest that CCOMT does not significantly contribute to the 3-O-methylation step in S lignin biosynthesis in alfalfa and that there is redundancy with respect to the 3-O-methylation reaction of G lignin biosynthesis. COMT is unlikely to catalyze the in vivo methylation of caffeic acid during lignin biosynthesis.
在菜豆苯丙氨酸解氨酶PAL2启动子的控制下,构建了携带咖啡酸3 - O -甲基转移酶(COMT)和咖啡酰辅酶A 3 - O -甲基转移酶(CCOMT)cDNA序列的转基因苜蓿植株。COMT的强烈下调导致木质素含量降低,总愈创木基(G)木质素单元减少,单体和二聚体木质素降解产物中丁香基(S)单元几乎完全丧失,以及低水平的5 - 羟基愈创木基单元和一种新型二聚体出现。没有可溶性单木质醇前体积累。相比之下,CCOMT的强烈下调导致木质素水平降低,G单元减少而S单元不减少,并且G单元的β-5连接二聚体增加。可溶性咖啡酸β - d -葡萄糖苷仅在CCOMT下调的植株中积累。结果表明,CCOMT对苜蓿S木质素生物合成中的3 - O -甲基化步骤贡献不大,并且在G木质素生物合成中3 - O -甲基化反应存在冗余。COMT不太可能在木质素生物合成过程中催化咖啡酸的体内甲基化。