An aromatic substrate prenyltransferase involved in the chemical diversification of flavonoids in Glycyrrhiza glabra.

Using cultured Glycyrrhiza glabra roots, we identified a new prenyltransferase involved in the formation of a variety of flavonoids, thereby revealing novel prenylated isoflavonoid pathways in licorice. Prenylated isoflavonoids are widely distributed specialized metabolites within the Fabaceae and contribute to various characteristic biological activities in both plants and humans. Several aromatic prenyltransferases (PTs) have been identified in Glycyrrhiza species, which are the most widely consumed crude drugs in traditional Chinese medicine. However, these enzymes do not sufficiently explain the structural diversity of prenylated flavonoids produced by the Glycyrrhiza genus. To identify additional novel PTs, we used elicited cultured Glycyrrhiza glabra roots as source material, where elicitor treatment increased the accumulation of multiple prenylated flavonoids. To identify the responsible enzyme, PT candidates were screened using G. uralensis transcriptomes, currently the sole publicly available transcriptomic resource within the genus, and a homolog designated GgBSPT1 (BSPT; a broad-substrate prenyltransferase) was subsequently isolated from elicited cultured G. glabra roots. GgBSPT1 differed from previously identified Glycyrrhiza PTs in both amino acid sequence and enzymatic properties. GgBSPT1 displayed unusually broad substrate acceptance across 20 distinct flavonoid structures and catalyzed regiospecific 3'-prenylation of isoliquiritigenin and 6-prenylation of five flavonoids. Overall, elicited cultured G. glabra roots enabled the identification of a previously unrecognized PT that is functionally distinct from earlier reported Glycyrrhiza PTs. This study provides new insights into the metabolic plasticity of Glycyrrhiza species and expands the enzymatic toolkit for future metabolic engineering of prenylated phytochemicals through the unusually broad substrate specificity of GgBSPT1.