The Preiss-Handler pathway, which salvages nicotinate (NA) for NAD synthesis, 34 is an indispensable biochemical pathway in land plants. Various NA conjugations 35 (mainly methylation and glycosylation) have been detected, and have long been 36 proposed for NA detoxification in plants. Previously, we demonstrated that NA O37 glucosylation functions as a mobilizable storage form for NAD biosynthesis in the 38 Brassicaceae. However, little is known about the functions of other NA 39 conjugations in plants. In this study, we firstly found that N-methylnicotinate is a 40 ubiquitous NA conjugation in land plants. Further, we functionally identified a 41 novel methyltransferase (At3g53140, NANMT), which is mainly res... More
The Preiss-Handler pathway, which salvages nicotinate (NA) for NAD synthesis, 34 is an indispensable biochemical pathway in land plants. Various NA conjugations 35 (mainly methylation and glycosylation) have been detected, and have long been 36 proposed for NA detoxification in plants. Previously, we demonstrated that NA O37 glucosylation functions as a mobilizable storage form for NAD biosynthesis in the 38 Brassicaceae. However, little is known about the functions of other NA 39 conjugations in plants. In this study, we firstly found that N-methylnicotinate is a 40 ubiquitous NA conjugation in land plants. Further, we functionally identified a 41 novel methyltransferase (At3g53140, NANMT), which is mainly responsible for N42 methylnicotinate formation, from Arabidopsis. We also established that 43 trigonelline (Tg) is a detoxification form of endogenous NA in plants. Combined 44 phylogenetic analysis and enzymatic assays revealed that NA N-methylation 45 activity was likely derived from duplication and subfunctionalization of an 46 ancestral caffeic acid O-methyltransferase (COMT) gene in the course of land 47 plant evolution. COMT enzymes, which function in S-lignin biosynthesis, also 48 have weak NANMT activity. Our data suggest that NA detoxification conferred by 49 NANMT and COMT might have facilitated the retention of the Preiss-Handler 50 pathway in land plants.
