P450s and UGTs: Key Players in the Structural Diversity of Triterpenoid Saponins

Abstract

The recent spread of next-generation sequencing techniques has facilitated transcriptome analyses of non-model plants. As a result, many of the genes encoding enzymes related to the production of specialized metabolites have been identified. Compounds derived from 2,3-oxidosqualene (the common precursor of sterols, steroids and triterpenoids), a linear compound of 30 carbon atoms produced through the mevalonate pathway, are called triterpenes. These include essential sterols, which are structural components of biomembranes; steroids such as the plant hormones, brassinolides and the toxin in potatoes, solanine; as well as the structurally diverse triterpenoids. Triterpenoids containing one or more sugar moieties attached to triterpenoid aglycones are called triterpenoid saponins. Triterpenoid saponins have been shown to have various medicinal properties, such as anti-inflammatory, anticancerogenic and antiviral effects. This review summarizes the recent progress in gene discovery and elucidates the biochemical functions of biosynthetic enzymes in triterpenoid saponin biosynthesis. Special focus is placed on key players in generating the structural diversity of triterpenoid saponins, cytochrome P450 monooxygenases (P450s) and the UDP-dependent glycosyltransferases (UGTs). Perspectives on further gene discovery and the use of biosynthetic genes for the microbial production of plant-derived triterpenoid saponins are also discussed.

Spatial transcriptome analysis provides insights of key gene(s) involved in steroidal saponin biosynthesis in medicinally important herb Trillium govanianum

“…Identification of large numbers of DEGs in pair-wise comparisons suggests considerable transcriptional differences among tissues of T. govanianum. Additionally, important CYPs and UGTs reported to be involved in secondary metabolites biosynthesis including steroidal saponins23, showed differential expression among all the tissues supporting spatial metabolite biosynthesis in this plant. The expression analysis revealed that maximum numbers of genes were highly expressed in leaf and fruit tissues, indicating active biosynthesis of steroidal saponin in these tissues.…”

“…In plants, cycloartenol synthase and lanosterol synthase mediates the cyclization of 2,3-oxidosqualene to synthesize steroidal saponins202122. Further, several hydroxylation and glycosylation steps catalyzed by CYP450s and UGTs respectively, contributes to the structural and functional diversification of various steroidal saponins23.…”

Multi‐tissue integration of transcriptomic and specialized metabolite profiling provides tools for assessing the common bean (Phaseolus vulgaris) metabolome

“…The lack of incorporation of the labeled phenylalanine into saponins is probably due to the different biosynthetic origin of these molecules. Triterpene saponins are derived from the mevalonate isoprenoid pathway, and their diversity is achieved through subsequent modifications of aglycone downstream of 2,3‐oxidosqualene cyclization (Seki et al ., ). Further support to our proposed pathways for saponin biosynthesis in Phaseolus would therefore require the use of a different labeled precursor (e.g., labeled mevalonate; Trojanowska et al ., ).…”

Novel triterpene oxidizing activity of Arabidopsis thaliana CYP716A subfamily enzymes

“…UGTs are reportedly involved in triterpenoid biosynthesis in plants [22,25]. Among them, P450s have been described as the key players in diversifying triterpenoid scaffolds, and were recently identified in many triterpenoid-producing plant species [22].…”