Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, OK 73401, USA.
Proc Natl Acad Sci U S A. 2010 Oct 12;107(41):17803-8. doi: 10.1073/pnas.1012900107. Epub 2010 Sep 27.
Cinnamoyl CoA reductases (CCR) convert hydroxycinnamoyl CoA esters to their corresponding cinnamyl aldehydes in monolignol biosynthesis. We identified two CCR genes in the model legume Medicago truncatula. CCR1 exhibits preference for feruloyl CoA, but CCR2 prefers caffeoyl and 4-coumaroyl CoAs, exhibits sigmoidal kinetics with these substrates, and is substrate-inhibited by feruloyl and sinapoyl CoAs. M. truncatula lines harboring transposon insertions in CCR1 exhibit drastically reduced growth and lignin content, whereas CCR2 knockouts grow normally with moderate reduction in lignin levels. CCR1 fully and CCR2 partially complement the irregular xylem gene 4 CCR mutation of Arabidopsis. The expression of caffeoyl CoA 3-O-methyltransferase (CCoAOMT) is up-regulated in CCR2 knockout lines; conversely, knockout of CCoAOMT up-regulates CCR2. These observations suggest that CCR2 is involved in a route to monolignols in Medicago whereby coniferaldehyde is formed via caffeyl aldehyde which then is 3-O-methylated by caffeic acid O-methyltransferase.
肉桂酰辅酶 A 还原酶（CCR）在木质素生物合成中将羟基肉桂酰辅酶 A 酯转化为相应的肉桂基醛。我们在模式豆科植物蒺藜苜蓿中鉴定出两个 CCR 基因。CCR1 对阿魏酰辅酶 A 表现出偏好，但 CCR2 更喜欢咖啡酰辅酶 A 和 4-香豆酰辅酶 A，对这些底物表现出 S 型动力学，并被阿魏酰辅酶 A 和芥子酰辅酶 A 抑制。携带 CCR1 转座子插入的蒺藜苜蓿系表现出严重的生长和木质素含量降低，而 CCR2 敲除系生长正常，木质素水平适度降低。CCR1 完全和 CCR2 部分互补拟南芥不规则木质素基因 4 CCR 突变。CCoAOMT（咖啡酰辅酶 A 3-O-甲基转移酶）的表达在 CCR2 敲除系中上调；相反，CCoAOMT 的敲除上调了 CCR2。这些观察结果表明，CCR2 参与了蒺藜苜蓿中单宁醇形成的途径，其中松柏醛通过咖啡醛形成，然后由咖啡酸 O-甲基转移酶 3-O-甲基化。
