Li Wei, Zhang Fengxia, Wu Ranran, Jia Lijia, Li Guosheng, Guo Yalong, Liu Cuimin, Wang Guodong
State Key Laboratory of Plant Genomics and National Center for Plant Gene Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
State Key Laboratory of Plant Cell and Chromosome Engineering and Center for Molecular Agrobiology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
Plant Physiol. 2017 Jul;174(3):1492-1504. doi: 10.1104/pp.17.00259. Epub 2017 May 22.
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 -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 first found that -methylnicotinate is a ubiquitous NA conjugation in land plants. Furthermore, we functionally identified a novel methyltransferase (At3g53140; NAMT), which is mainly responsible for -methylnicotinate formation, from Arabidopsis (). We also established that trigonelline is a detoxification form of endogenous NA in plants. Combined phylogenetic analysis and enzymatic assays revealed that NA -methylation activity was likely derived from the duplication and subfunctionalization of an ancestral caffeic acid -methyltransferase () gene in the course of land plant evolution. COMT enzymes, which function in -lignin biosynthesis, also have weak NAMT activity. Our data suggest that NA detoxification conferred by NAMT and COMT might have facilitated the retention of the Preiss-Handler pathway in land plants.
普赖斯-汉德勒途径可挽救烟酸（NA）用于合成烟酰胺腺嘌呤二核苷酸（NAD），是陆地植物中不可或缺的生化途径。已检测到多种NA缀合物（主要是甲基化和糖基化），长期以来人们一直认为它们在植物中用于NA解毒。此前，我们证明了NA糖基化在十字花科植物中作为NAD生物合成的可动员储存形式发挥作用。然而，关于植物中其他NA缀合物的功能知之甚少。在本研究中，我们首先发现β-甲基烟酸是陆地植物中普遍存在的NA缀合物。此外，我们从拟南芥中功能鉴定了一种新型甲基转移酶（At3g53140；NAMT），它主要负责β-甲基烟酸的形成。我们还确定葫芦巴碱是植物中内源性NA的解毒形式。系统发育分析和酶活性测定相结合表明，NA甲基化活性可能源于陆地植物进化过程中一个祖先咖啡酸O-甲基转移酶（COMT）基因的复制和亚功能化。在木质素生物合成中起作用的COMT酶也具有较弱的NAMT活性。我们的数据表明，NAMT和COMT赋予的NA解毒作用可能促进了普赖斯-汉德勒途径在陆地植物中的保留。
