AUTHOR=Liu Lingyun , Zhang Fengxia , Li Guosheng , Wang Guodong 

TITLE=Qualitative and Quantitative NAD+ Metabolomics Lead to Discovery of Multiple Functional Nicotinate N-Glycosyltransferase in Arabidopsis

JOURNAL=Frontiers in Plant Science

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.01164

DOI=10.3389/fpls.2019.01164

ISSN=1664-462X

ABSTRACT=<p>The Preiss-Handler pathway, which salvages nicotinate (NA) for NAD synthesis, is a conserved biochemical pathway in land plants. We previously demonstrated that various NA conjugations (mainly methylation and glycosylation) shared the NA detoxification function in all tested plants. It remains unclear whether other NA conjugates with low abundance exist in plants. In this study, we discovered at least two additional NA <italic>N</italic>-glycosides in <italic>Arabidopsis</italic>, which was tentatively elucidated as nicotinate <italic>N</italic>-pentoside (Na<italic>N</italic>P) and NA <italic>N</italic>-rhamoside (Na<italic>N</italic>Rha), using liquid chromatography triple-quadrupole mass spectrometry (LC-QQQ-MS) with precursor ion-scanning (PreIS). We further quantitatively profile the NAD<sup>+</sup>-related metabolites in 24 tissues of <italic>Arabidopsis</italic>. Biochemical assays of UGT76C family revealed that UGT76C5 (encoded by <italic>At5g05890</italic>, previously identified as Na<italic>N</italic>GT) was a multiple functional nicotinate <italic>N</italic>-glycosyltransferase, with high preference to UDP-xylose and UDP-arabinose. The deficiency of Na<italic>N</italic>P and Na<italic>N</italic>Rha in <italic>ugt76c5</italic> mutant suggested that UGT76C5 is responsible for biosynthesis of Na<italic>N</italic>P and Na<italic>N</italic>Rha <italic>in planta</italic>. We also identify one amino acid difference in PSPG (plant secondary product glycosyltransferase) motif is responsible for the divergence of Na<italic>N</italic>GT (UGT76C4) and UGT76C5. Taken together, our study not only identifies a novel nicotinate <italic>N</italic>-glycosyltransferase but also paves the way for investigations of the <italic>in planta</italic> physiological functions of various NA conjugations.</p>