Tea plants (Camellia sinensis) store volatile organic compounds (VOCs; monoterpene, aromatic, and aliphatic alcohols) in the leaves in the form of water-soluble diglycosides, primarily as b-primeverosides (6-O-b-D-xylopyranosyl-b-D-glucopyranosides). These VOCs play a critical role in plant defenses and tea aroma quality, yet little is known about their biosynthesis and physiological roles in planta. Here, we identified two UDP-glycosyltransferases (UGTs) from C. sinensis, UGT85K11 (CsGT1) and UGT94P1 (CsGT2), converting VOCs into b-primeverosides by sequential glucosylation and xylosylation, respectively. CsGT1 exhibits a broad substrate specificity toward monoterpene, aromatic, and aliphatic alcohols to produce the respective glucosides. On the other hand, CsGT2 specifically catalyzes the xylosylation of the 69-hydroxy group of the sugar moiety of geranyl b-D-glucopyranoside, producing geranyl b-primeveroside. Homology modeling, followed by site-directed mutagenesis of CsGT2, identified a unique isoleucine-141 residue playing a crucial role in sugar donor specificity toward UDP-xylose. The transcripts of both CsGTs were mainly expressed in young leaves, along with b-PRIMEVEROSIDASE encoding a diglycoside-specific glycosidase. In conclusion, our findings reveal the mechanism of aroma b-primeveroside biosynthesis in C. sinensis. This information can be used to preserve tea aroma better during the manufacturing process and to investigate the mechanism of plant chemical defenses.
Tea plant (Camellia sinensis) biosynthesizes a wide variety of specialized metabolites, including phenolic compounds such as catechins. Flavonol, one of the major flavonoid subclasses, in C. sinensis is present in the O-glycoside form, such as quercetin 3-O-β-D-glucopyranoside, kaempferol 3-O-β-D-glucopyranoside, and rutin (quercetin 3-O-β-glucopyranosyl-6-O-α-rhamnoside). These flavonol glycosides are highly accumulated, constituting up to 2-3% (w/w dry weight) of tea leaves; however, their biosynthetic machinery in C. sinensis remains elusive. Using high-throughput RNA sequencing from the fresh leaves of a cultivar (C. sinensis var sinensis cv Yabukita) and rapid amplification of cDNA ends (RACE) cloning with degenerate oligonucleotide primers, we identified a full-length cDNA of UDP-glycosyltransferase, designated as UGT73A17, and characterized the biochemical and molecular functions of UGT73A17. Recombinant UGT73A17 protein catalyzed 3-O-glucosylation of quercetin, yielding quercetin 3-O-β-D-glucopyranoside in vitro. The preferential expression of UGT73A17 gene in the mature, relative to young leaves, stems and roots, is roughly consistent with the accumulation pattern of flavonol glycosides in C. sinensis, suggesting that UGT73A17, in part, participates in the biosynthesis of flavonol glycosides in planta.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.