Our Research Outline
1) Plant volatile biosynthesis and glycosylation
Plants emit volatile organic compounds (VOCs), such as monoterpenes (C10), sesquiterpenes (C15), phenylpropanoids (C9), norisoprenoids (C16), aromatic esters, or green leaf alcohols (C6), in response to attacks by insect herbivores, mechanical wounding, or endogenous developmental cues. In general, VOCs are considered not only to be chemical defense compounds transmitting biological signals to the environment ( but also important commercial products, because they influence the quality and character of dietary foods and beverages as aromas.
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 β-primeverosides (6-O–β–D-xylopyranosyl-β–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 β-primeverosidesby 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 6′-hydroxy group of the sugar moiety of geranyl β–D-glucopyranoside, producing geranyl β-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 β-primeverosidase encoding a diglycoside-specific glycosidase. In conclusion, our findings reveal the mechanism of aroma β-primeverosidebiosynthesis 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.