Downregulation of caffeic acid 3-O-methyltransferase and caffeoyl CoA 3-O-methyltransferase in transgenic alfalfa:: Impacts on lignin structure and implications for the biosynthesis of G and S lignin
Downregulation of caffeic acid 3-O-methyltransferase and caffeoyl CoA 3-O-methyltransferase in transgenic alfalfa:: Impacts on lignin structure and implications for the biosynthesis of G and S lignin
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DOI：
10.1105/tpc.13.1.73
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发表时间：
2001-01-01
期刊：
影响因子：
11.6
通讯作者：
Dixon, RA
中科院分区：
文献类型：
--
作者：
Guo, DJ;Chen, F;Dixon, RA
转基因苜蓿植物的产生，窝藏咖啡酸3-O-甲基转移酶（COMT）和咖啡酰CoA 3-O-甲基转移酶（CCOMT）的cDNA序列的控制下，豆苯丙氨酸解氨酶PAL 2启动子。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的胡萝卜基（S）单元几乎全部损失，以及出现低水平的5-羟基愈创木基单元和新的二聚体。无可溶性单细胞前体积累。相反，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，以及G单元的β-5连接二聚体增加。可溶性咖啡酸P-D-葡萄糖苷的积累只发生在CCOMT下调的植物中。结果表明，CCOMT对苜蓿S木质素生物合成中的3-O-甲基化反应没有显著贡献，而对G木质素生物合成中的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。
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 P-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.