A noncanonical vacuolar sugar transferase required for biosynthesis of antimicrobial defense compounds in oat

Orme, Anastasia, Louveau, Thomas, Stephenson, Michael J. ORCID: https://orcid.org/0000-0002-2594-1806, Appelhagen, Ingo, Melton, Rachel, Cheema, Jitender, Li, Yan, Zhao, Qiang, Zhang, Lei, Fan, Danlin, Tian, Qilin, Vickerstaff, Robert J., Langdon, Tim, Han, Bin and Osbourn, Anne (2019) A noncanonical vacuolar sugar transferase required for biosynthesis of antimicrobial defense compounds in oat. Proceedings of the National Academy of Sciences of the United States of America, 116 (52). pp. 27105-27114. ISSN 0027-8424

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Abstract

Plants produce an array of natural products with important ecological functions. These compounds are often decorated with oligosaccharide groups that influence bioactivity, but the biosynthesis of such sugar chains is not well understood. Triterpene glycosides (saponins) are a large family of plant natural products that determine important agronomic traits, as exemplified by avenacins, antimicrobial defense compounds produced by oats. Avenacins have a branched trisaccharide moiety consisting of L-arabinose linked to 2 D-glucose molecules that is critical for antifungal activity. Plant natural product glycosylation is usually performed by uridine diphosphate-dependent glycosyltransferases (UGTs). We previously characterized the arabinosyltransferase that initiates the avenacin sugar chain; however, the enzymes that add the 2 remaining D-glucose molecules have remained elusive. Here we characterize the enzymes that catalyze these last 2 glucosylation steps. AsUGT91G16 is a classical cytosolic UGT that adds a 1,2-linked D-glucose molecule to L-arabinose. Unexpectedly, the enzyme that adds the final 1,4-linked D-glucose (AsTG1) is not a UGT, but rather a sugar transferase belonging to Glycosyl Hydrolase family 1 (GH1). Unlike classical UGTs, AsTG1 is vacuolar. Analysis of oat mutants reveals that AsTG1 corresponds to Sad3, a previously uncharacterized locus shown by mutation to be required for avenacin biosynthesis. AsTG1 and AsUGT91G16 form part of the avenacin biosynthetic gene cluster. Our demonstration that a vacuolar transglucosidase family member plays a critical role in triterpene biosynthesis highlights the importance of considering other classes of carbohydrate-active enzymes in addition to UGTs as candidates when elucidating pathways for the biosynthesis of glycosylated natural products in plants.

Item Type: Article
Additional Information: Data Availability: Data deposition: Raw and assembled RNA-seq data can be accessed at http://db.ncgr.ac.cn/oat/RNAseq.php. Sequences have been deposited in the GenBank database (accession nos. MN396758–MN396761). This work was supported by the UK Biological Sciences Research Council (BBSRC) Doctoral Training Programme (A. Orme); the joint Engineering and Physical Sciences Research Council/Biotechnological and BBSRC-funded OpenPlant Synthetic Biology Research Centre Grant BB/L014130/1 (to M.J.S. and A. Osbourn); the Centre of Excellence for Plant and Microbial Sciences, established between the John Innes Centre and the Chinese Academy of Sciences and funded by the BBSRC and the Chinese Academy of Sciences; National Natural Science Foundation of China Grant 31788103, “Molecular Design for Future Crops” (to B.H.); BBSRC Strategic Programme Grant BB/P012523/1, “Molecules from Nature”; and the John Innes Foundation (A. Osbourn and R.M.).
Faculty \ School: Faculty of Science > School of Biological Sciences
Faculty of Science > School of Chemistry
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Depositing User: LivePure Connector
Date Deposited: 26 Sep 2022 13:33
Last Modified: 24 Oct 2022 06:53
URI: https://ueaeprints.uea.ac.uk/id/eprint/88650
DOI: 10.1073/pnas.1914652116

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