Diterpenoid UDP-Glycosyltransferases from Chinese Sweet Tea and Ashitaba Complete the Biosynthesis of Rubusoside

Abstract

Diterpenoids are important molecules that play significant roles in many biological processes. In plants, acyclic diterpene phytol is a representative side chain of chlorophyll, and tetracyclic diterpene gibberellins ubiquitously serve as plant hormones regulating growth and development. Decoration of diterpene core structures by oxidation and glycosylation are usually key steps to confer final bioactivity of diterpenoid compounds. In contrast to the extensively studied oxidases involved in gibberellin biosynthesis, diterpenoid-related glycosyltransferases have been scarcely documented, possibly due to the relative rarity of diterpene glycosides in the plant kingdom. Only a few UDPdependent glycosyltransferases (UGTs) have been characterized to participate in diterpene glycoside biosynthesis (Richman et al., 2005;Nagatoshi et al., 2012).Rubusoside is an important ent-kaurene-type diterpenoid glycoside mainly produced by two edible and medicinal plants of Rubus suavissimus (also called ''Chinese sweet tea'') and Angelica keiskei (also called ''Ashitaba'' in Japanese) (Tanaka et al., 1981;Zhou et al., 2012). The leaves of both plants have a long history of being collected by local people to make herbal tea due to their natural sweetness or putative therapeutic activities.Rubusoside is approximately 60 times as sweet as sucrose (Tanaka et al., 1981) and has less bitter aftertaste. Recently, it was also reported as the first molecule that inhibited both human fructose transporter GLUT5 and glucose transporter GLUT1 (Thompson et al., 2015). The biosynthesis of rubusoside is proposed to resemble that of the steviol glycosides (SGs) occurring in Stevia rebaudiana (Ceunen and Geuns, 2013). Steviol generated by oxidation of the ent-kaurene skeleton serves as a common aglycone for all SGs compounds. Further glycosylation via UGT-mediating decorations produce rubusoside and related glycosides (Supplemental Figure 1).

Functional genomics analysis reveals two novel genes required for littorine biosynthesis

“…f). Many UGTs catalyse the glycosylation of substrates with similar structures (Lim et al , ; Torrens‐Spence et al , ; Sun et al , ). UGT1 in this study may not be the only UGT to produce phenyllactylglucose from phenyllactate, as other uncharacterized A. belladonna UGTs may also produce phenyllactylglucose in a small amount for littorine biosynthesis.…”

UDP-glucosyltransferase regulates grain size and abiotic stress tolerance associated with metabolic flux redirection in rice

“…Previous studies have indicated that the amino acids in the Nterminal region of UGTs contribute to the regio-specificity of sugar acceptors and that the PSPG box in the C-terminal region of UGTs plays a key role in sugar-donor binding 43,44 . The metabolomics data described above showed that levels of kaempferol, naringenin, quercetin and monolignols were higher in NIL-GSA1 CG14 than in NIL-GSA1 WYJ , whereas the levels of naringenin-7-O-glucoside, quercetin-7-O-glucoside and lignin were significantly lower.…”

Contribution of phenylpropanoid metabolism to plant development and plant–environment interactions

“…Phenylpropanoid homeostasis among different branches of phenylpropanoid metabolism, which is achieved via the regulation of metabolic flux redirection (MFR), exhibits extraordinary complexity and high‐level plasticity during successive developmental stages and in response to environmental stimuli and changes (Lanot et al, 2008). In the last few decades, a considerable number of studies have unraveled the sophisticated mechanisms that control the biosynthesis of phenylpropanoid metabolites and the regulation of the phenylpropanoid pathway at multiple levels (Figure 1); these studies have led to a comprehensive understanding of phenylpropanoid metabolism and provide the theoretical basis for the genetic improvement of plants and de novo artificial production of metabolites that are beneficial for human health and that meet the demands for horticulture, industry, and agriculture (Lau and Sattely, 2015; Liu et al, 2018; Sun et al, 2018b; Chanoca et al, 2019; Halpin, 2019).…”