A Novel N-Methyltransferase in Arabidopsis Appears to Feed a Conserved Pathway for Nicotinate Detoxification among Land Plants and Is Associated with Lignin Biosynthesis

摘要

The Preiss-Handler pathway, which salvages nicotinate () for NAD synthesis, is an indispensable biochemical pathway in land plants. Various conjugations (mainly methylation and glycosylation) have been detected and have long been proposed for detoxification in plants. Previously, we demonstrated that O-glucosylation functions as a mobilizable storage form for NAD biosynthesis in the Brassicaceae. However, little is known about the functions of other conjugations in plants. In this study, we first found that N-methylnicotinate is a ubiquitous conjugation in land plants. Furthermore, we functionally identified a novel methyltransferase (At3g53140; NANMT), which is mainly responsible for N-methylnicotinate formation, from Arabidopsis (Arabidopsis thaliana). We also established that trigonelline is a detoxification form of endogenous in plants. Combined phylogenetic analysis and enzymatic assays revealed that N-methylation activity was likely derived from the 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 detoxification conferred by NANMT and COMT might have facilitated the retention of the Preiss-Handler pathway in land plants.