Plant Physiol:中科院遗传所王国栋研究组发表植物NAD补救合成途径
2017年5月22日，国际植物学顶级期刊《Plant Physiology》杂志上在线发表了中国科学院遗传与发育生物学研究所王国栋研究组题为“A novel N-methyltransferase in Arabidopsis appears to feed a conserved pathway for nicotinate detoxification among land plants and is associated with lignin biosynthesis”的研究论文。王国栋研究组的李伟博士，张凤霞博士和吴然然博士为该文章的共同第一作者，王国栋研究员为论文通讯作者。
NAD (尼克酰胺腺嘌呤二核苷酸) 作为电子传递载体(辅酶)参与众多的氧化还原反应而为广大研究人员所熟知。在植物NAD补救合成途径中(Preiss-Handler途径)，特异性存在尼克酸(nicotinate，NA)和多种NA的衍生物(糖基化，甲基化等)，但迄今为止，关于NA衍生物在植物代谢中的分子机制及其生理功能尚未有报道。
王国栋研究组前期的研究表明NA的O-位糖基化修饰可能保护植物细胞免受种子萌发过程中NA过度积累所造成的毒害，而且NAOGT活性是在十字花科植物进化过程中才逐渐获得，NAOGT活性的获得为植物适应环境提供选择优势(Li et al., Plant Cell, 2015)。最近，王国栋研究组发现在拟南芥是一类新型的N-甲基转移酶(NANMT，At3g53140编码)负责尼克酸N-甲基化化合物(又名葫芦巴碱)的生成，同时尼克酸N-甲基化修饰时植物解毒NA的另外一种形式。全面的进化和生化分析结果表明，这类新型的尼克酸N-甲基转移酶的功能来自参与植物木质素生物合成途径的COMT(咖啡酸O-甲基转移酶)基因的复制和功能分化。植物原始的COMT还保留微弱的NANMT活性，表明在植物漫长的进化过程中，NANMT活性的获得促成Preiss-Handler途径在陆生植物基因组得以保留的一个重要原因。
图. 陆生植物NANMT生化功能鉴定和进化轨迹分析。
原文链接：
A novel N-methyltransferase in Arabidopsis appears to feed a conserved pathway for nicotinate detoxification among land plants and is associated with lignin biosynthesis
原文摘要：
The Preiss-Handler pathway, which salvages nicotinate (NA) for NAD synthesis, is an indispensable biochemical pathway in land plants. Various NA conjugations (mainly methylation and glycosylation) have been detected, and have long been proposed for NA detoxification in plants. Previously, we demonstrated that NA O-glucosylation functions as a mobilizable storage form for NAD biosynthesis in the Brassicaceae. However, little is known about the functions of other NA conjugations in plants. In this study, we firstly found that N-methylnicotinate is a ubiquitous NA conjugation in land plants. Further, we functionally identified a novel methyltransferase (At3g53140, NANMT), which is mainly responsible for N-methylnicotinate formation, from Arabidopsis. We also established that trigonelline (Tg) is a detoxification form of endogenous NA in plants. Combined phylogenetic analysis and enzymatic assays revealed that NA N-methylation activity was likely derived from duplication and subfunctionalization of an ancestral caffeic acid O-methyltransferase (COMT) gene in the course of land plant evolution. COMT enzymes, which function in S-lignin biosynthesis, also have weak NANMT activity. Our data suggest that NA detoxification conferred by NANMT and COMT might have facilitated the retention of the Preiss-Handler pathway in land plants.
作者：王国栋
