Abstract
Glycosylation of small molecules is critical for numerous biological processes in plants, including hormone homeostasis, neutralization of xenobiotics, and synthesis and storage of specialized metabolites. Glycosylation of plant natural products is usually performed by uridine diphosphate-dependent glycosyltransferases (UGTs). Triterpene glycosides (saponins) are a large family of plant natural products that determine important agronomic traits such as disease resistance and flavor and have numerous pharmaceutical applications. Most characterized plant natural product UGTs are glucosyltransferases, and little is known about enzymes that add other sugars. Here we report the discovery and characterization of AsAAT1 (UGT99D1), which is required for biosynthesis of the antifungal saponin avenacin A-1 in oat (Avena strigosa). This enzyme adds l-Ara to the triterpene scaffold at the C-3 position, a modification critical for disease resistance. The only previously reported plant natural product arabinosyltransferase is a flavonoid arabinosyltransferase from Arabidopsis (Arabidopsis thaliana). We show that AsAAT1 has high specificity for UDP-β-l-arabinopyranose, identify two amino acids required for sugar donor specificity, and through targeted mutagenesis convert AsAAT1 into a glucosyltransferase. We further identify a second arabinosyltransferase potentially implicated in the biosynthesis of saponins that determine bitterness in soybean (Glycine max). Our investigations suggest independent evolution of UDP-Ara sugar donor specificity in arabinosyltransferases in monocots and eudicots.
Highlights
Plants produce a huge array of natural products, many of which are glycosylated (Vetter, 2000; Vincken et al, 2007; Liu et al, 2013)
To identify candidate uridine diphosphate-dependent glycosyltransferases (UGTs) implicated in avenacin biosynthesis, we mined an oat root tip transcriptome database that we generated previously (Kemen et al, 2014) using BLAST analysis
UGTs belonging to the carbohydrate-active enzyme (CAZY) GT1 family are critical for small molecule glycosylation in plants
Summary
Plants produce a huge array of natural products, many of which are glycosylated (Vetter, 2000; Vincken et al, 2007; Liu et al, 2013). Glycosylation can play a major role in the structural diversification of secondary metabolites. Over 300 glycosides have been reported for the simple flavonol quercetin alone (Reuben et al, 2006). Glycosylation modifies the reactivity and solubility of the corresponding aglycones, so influences cellular localization and bioactivity (Augustin et al, 2011; Liu et al, 2013). Plant natural products are decorated with a variety of different types of individual sugars and oligosaccharide chains.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
