Saponin Biosynthesis in Saponaria vaccaria. cDNAs Encoding β-Amyrin Synthase and a Triterpene Carboxylic Acid Glucosyltransferase

Abstract

Saponaria vaccaria (Caryophyllaceae), a soapwort, known in western Canada as cowcockle, contains bioactive oleanane-type saponins similar to those found in soapbark tree (Quillaja saponaria; Rosaceae). To improve our understanding of the biosynthesis of these saponins, a combined polymerase chain reaction and expressed sequence tag approach was taken to identify the genes involved. A cDNA encoding a β-amyrin synthase (SvBS) was isolated by reverse transcription-polymerase chain reaction and characterized by expression in yeast (Saccharomyces cerevisiae). The SvBS gene is predominantly expressed in leaves. A S. vaccaria developing seed expressed sequence tag collection was developed and used for the isolation of a full-length cDNA bearing sequence similarity to ester-forming glycosyltransferases. The gene product of the cDNA, classified as UGT74M1, was expressed in Escherichia coli, purified, and identified as a triterpene carboxylic acid glucosyltransferase. UGT74M1 is expressed in roots and leaves and appears to be involved in monodesmoside biosynthesis in S. vaccaria.

Glycosyltransferases from Oat (Avena) Implicated in the Acylation of Avenacins

“…3. Other characterized UGT74 enzymes include an indole-3-acetic acid GT (ZmIAGT) from Z. mays (21), a crocetin GT (CsUGT2) from Crocus sativus (22), a gentisic acid xylosyltransferase from Solanum lycopersicum (SlGAGT) (23), a salicylic acid GT from Nicotiana tabacum (NtSAGTase) (24), a salicylic acid/anthranilic acid GT (UGT74F2), a thiohydroximate GT (AtUGT74B1) and a jasmonate GT (AtUGT74D1) from A. thaliana (25)(26)(27), and a triterpene GT from Saponaria vaccaria (synonym Vaccaria hispanica) (SvUGT74M1) that catalyzes the addition of glucose onto gypsogenic acid (28). A. thaliana UGT74E2 is thought to be an auxin indole-3-butyric acid glucosyltransferase (29) and UGT74C1 is implicated in aliphatic glucosinolate biosynthesis (30).…”

<strong>Multi-scale analysis of structural variability of Caryophyllaceae saponins by a simplex machine learning approach</strong>

“…For a same aglycone, global variation trends between substituted sugars significantly varied with molecular GLs: In Gyp, 28-Glc showed a strong peak under low molecular GL (GL=1) followed by rapid decrease to minimum in higher GLs (GL=2, 3, 4) (Figure 1b). This highlightedstrong contribution of early 28-Glc in ramification process (monodesmosylation) ofGyp leading to preliminary structural diversification of saponins [3,5,6]. In QA, 28-Glc seemed to play intermediate modulatory role due to its low relative levels in GLs = 1 and 4 (figure 1c).…”

“…Although Gyp and QA plots showed spatial neighboring (compared to GA), they differed by dispersions, inclinations and internal organization of corresponding clouds of points: relationship between 3-Xyl and 3-Gal showed significantly higher dispersion in QA than in Gyp (Figure1b). This aspect indicated wider regulation range of 3-Gal in QA compared to Gyp [3]. However, for (28-Xyl vs 28-Glc), the two aglycones showed opposite relationship leading to inversely inclined clouds of points: (global positive trend in QA against negative trend in Gyp) (Figure1a).…”

“…This could be linked to the occurrence of two carboxylic groups in GA(23-and 28-COOH) vs only one (28-COOH) in both QA and Gyp. Specific space of GA was characterized by strong relative 28-Glc levels (0.65-0.75) without competing (comparable) levels from other sugars in both C3 and C28 (Figure1a) [1,3,4]. Gyp occupied intermediate position between GA and QA whereas QA was the most distant from GA (Figure1a, 2b).Relative locations of different aglycones-based saponins in simulated graphicswere compatible with the metabolism: Gyp is metabolically precursor of both QA and GA (by 16-and 23-hydroxylation, respectively); this is compatible with intermediate position of Gypbetween QA and GA (competing for Gyp) [3].…”

“…Specific space of GA was characterized by strong relative 28-Glc levels (0.65-0.75) without competing (comparable) levels from other sugars in both C3 and C28 (Figure1a) [1,3,4]. Gyp occupied intermediate position between GA and QA whereas QA was the most distant from GA (Figure1a, 2b).Relative locations of different aglycones-based saponins in simulated graphicswere compatible with the metabolism: Gyp is metabolically precursor of both QA and GA (by 16-and 23-hydroxylation, respectively); this is compatible with intermediate position of Gypbetween QA and GA (competing for Gyp) [3]. Although Gyp and QA plots showed spatial neighboring (compared to GA), they differed by dispersions, inclinations and internal organization of corresponding clouds of points: relationship between 3-Xyl and 3-Gal showed significantly higher dispersion in QA than in Gyp (Figure1b).…”