Key Laboratory of Chemical Biology of Natural Products, Ministry of Education, School of Pharmaceutical Sciences, Shandong University, No. 44 West Wenhua Road, Jinan 250012, China.
Plant Physiol Biochem. 2013 Sep;70:133-41. doi: 10.1016/j.plaphy.2013.05.027. Epub 2013 May 31.
Cinnamyl alcohol dehydrogenase (CAD) (EC 1.1.1.195) is a key enzyme in lignin biosynthesis. It catalyzes cinnamyl aldehydes as substrates to form corresponding alcohols, the last step in monolignol biosynthesis. Almost all CAD members of land plants could be divided into three classes according to the phylogenetic analysis, together with gene structure and function. In the present investigation, two cDNAs encoding CADs were obtained from a Chinese liverwort Plagiochasma appendiculatum thallus library and were designated as PaCAD1 and PaCAD2. Phylogenetic analysis showed that PaCAD1 and PaCAD2 belonged to Class II. Full length cDNAs were heterologously expressed in E. coli and the recombinant PaCAD proteins displayed high activity levels using p-coumaryl, caffeyl, coniferyl, 5-hydroxyconiferyl and sinapyl aldehydes as substrates to form corresponding alcohols. The enzyme kinetics results showed that PaCAD1 and PaCAD2 used coniferyl aldehyde as the favourite substrate and showed high catalytic efficiency towards p-coumaryl aldehyde but lowest catalytic efficiency towards 5-hydroxyconiferaldehyde. In accord with the higher lignin content in the thallus than in the callus, the expression level of PaCAD2 was also higher in thallus than in the callus. The expression of PaCAD1 and PaCAD2 was induced by Methyl jasmonic acid (MeJA) treatment. This suggested that these two PaCADs played twin roles in lignin biosynthesis and the defencedefence of abiotic stress in P. appendiculatum. This is the first time that the CADs in liverworts have been functionally characterized.
肉桂醇脱氢酶（CAD）（EC 1.1.1.195）是木质素生物合成中的关键酶。它催化肉桂醛作为底物形成相应的醇，这是单体酚生物合成的最后一步。根据系统发育分析，几乎所有陆地植物的 CAD 成员都可以分为三类，同时还考虑了基因结构和功能。在本研究中，从中国地钱 Plagiochasma appendiculatum 叶状体文库中获得了两个编码 CAD 的 cDNA，并分别命名为 PaCAD1 和 PaCAD2。系统发育分析表明，PaCAD1 和 PaCAD2 属于第二类。全长 cDNA 在大肠杆菌中异源表达，重组 PaCAD 蛋白对 p-香豆酰基、咖啡酰基、松柏酰基、5-羟基松柏酰基和丁香醛基具有很高的活性水平，可形成相应的醇。酶动力学结果表明，PaCAD1 和 PaCAD2 以松柏醛基作为最喜爱的底物，对 p-香豆酰基醛具有很高的催化效率，但对 5-羟基松柏醛的催化效率最低。与叶状体比愈伤组织具有更高的木质素含量相一致，PaCAD2 在叶状体中的表达水平也高于愈伤组织。PaCAD1 和 PaCAD2 的表达受茉莉酸甲酯（MeJA）处理的诱导。这表明这两个 PaCAD 在木质素生物合成和地钱对非生物胁迫的防御中发挥着双重作用。这是首次对苔藓植物中的 CAD 进行功能表征。
