Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Glycosylation is a key modification that contributes to determine bioactivity and bioavailability of plant natural products, including that of terpenoids and steviol glycosides SVglys.
It is mediated by uridine-diphosphate glycosyltransferases UGTs , that achieve their activity by transferring sugars on small molecules. Thus, the diversity of SVglys is due to the number, the position and the nature of glycosylations on the hydroxyl groups in C and C of steviol. Despite the intense sweetener property of SVglys and the numerous studies conducted, the SVglys biosynthetic pathway remains largely unknown. After agroinfiltration-based transient gene expression in Nicotiana benthamiana , functionality of the recombinant UGT can be tested simply and directly in plants expressing it or from a crude extract.
The combined use of binary vectors from pGWBs series to produce expression vectors containing the stevia's UGT, enables functionality testing with many substrates as well as other applications for further analysis, including subcellular localization. GGDP then undergoes two cyclization steps, catalyzed by terpene cyclases to give ent -kaurene 5. Kaurenoic acid is the last step of a biosynthetic pathway shared by gibberellins and SVglys. Oxidation of KA leads to gibberellins, while its hydroxylation produces steviol that can be glycosylated on the two hydroxyl groups of its C and C to give SVglys.
To form steviol glycosides, UGTs transfer an activated sugar of a sugar-donor substrate on hydroxyl groups of an acceptor substrate. Glycosylation is a key and widespread modification of secondary metabolites, playing a pivotal role in the huge diversity of plant natural products 6.
Thus, more than 60 SVglys have been identified in S. The first part of the SVglys biosynthesis leading to steviol formation is well known and characterized 12 , The latter part, leading to SVglys from the steviol aglycone remains largely unknown as S. Nevertheless, several UGT genes of S. For example, 12 candidates have previously been identified In a more recent study, Li et al.
