Graduate School of Engineering Science, Akita University, Tegata Gakuen-machi 1-1, Akita City, Akita 010-0852, Japan.
Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, NY 14853, USA.
J Exp Bot. 2024 Mar 14;75(6):1671-1695. doi: 10.1093/jxb/erae011.
Lignin, flavonoids, melatonin, and stilbenes are plant specialized metabolites with diverse physiological and biological functions, supporting plant growth and conferring stress resistance. Their biosynthesis requires O-methylations catalyzed by 5-hydroxyconiferaldehyde O-methyltransferase (CAldOMT; also called caffeic acid O-methyltransferase, COMT). CAldOMT was first known for its roles in syringyl (S) lignin biosynthesis in angiosperm cell walls and later found to be multifunctional. This enzyme also catalyzes O-methylations in flavonoid, melatonin, and stilbene biosynthetic pathways. Phylogenetic analysis indicated the convergent evolution of enzymes with OMT activities towards the monolignol biosynthetic pathway intermediates in some gymnosperm species that lack S-lignin and Selaginella moellendorffii, a lycophyte which produces S-lignin. Furthermore, neofunctionalization of CAldOMTs occurred repeatedly during evolution, generating unique O-methyltransferases (OMTs) with novel catalytic activities and/or accepting novel substrates, including lignans, 1,2,3-trihydroxybenzene, and phenylpropenes. This review summarizes multiple aspects of CAldOMTs and their related proteins in plant metabolism and discusses their evolution, molecular mechanism, and roles in biorefineries, agriculture, and synthetic biology.
木质素、类黄酮、褪黑素和芪类化合物是具有多种生理和生物学功能的植物特化代谢物，它们支持植物生长并赋予植物抗逆性。它们的生物合成需要 5-羟基松柏醛 O-甲基转移酶（CAldOMT；也称为咖啡酸 O-甲基转移酶，COMT）催化的 O-甲基化。CAldOMT 最初因其在被子植物细胞壁中木质素的丁香基（S）生物合成中的作用而被人们所熟知，后来发现它具有多功能性。该酶还催化类黄酮、褪黑素和芪生物合成途径中的 O-甲基化。系统发育分析表明，一些裸子植物物种和石松属（Selaginella moellendorffii）中具有 OMT 活性的酶向单酚生物合成途径中间体的趋同进化，这些裸子植物缺乏 S-木质素，而石松属产生 S-木质素。此外，CAldOMTs 在进化过程中发生了多次新功能化，产生了具有新型催化活性和/或接受新型底物的独特 O-甲基转移酶（OMTs），包括木脂素、1,2,3-三羟基苯和苯丙烯。本综述总结了植物代谢中 CAldOMTs 及其相关蛋白的多个方面，并讨论了它们的进化、分子机制以及在生物炼制、农业和合成生物学中的作用。
