A BmMYB14 – UGT Regulatory Module Contributes to Dammarane-Type Triterpene Biosynthesis in Bacopa monnieri

Abstract

Bacosides, a key glycosylated dammarane-type triterpenes of Bacopa monnieri, exhibit diverse pharmacological activities, yet the enzymatic and regulatory mechanisms governing their biosynthesis remain underexplored. In this study, we functionally characterized the methyl jasmonate-inducible glycosyltransferase UGT94AV1 and demonstrated its ability to glycosylate diverse triterpenoid substrates, with the highest catalytic efficiency observed for ginsenoside RH2. Recombinant UGT94AV1 demonstrated a capacity for sequential glycosylation by efficiently catalyzing the transfer of a glucose moiety to the aglycone core, i.e., jujubogenin and pseudojujubogenin, derived from the periodate oxidation of bacoside A, and its corresponding monoglycosides. Overexpression of UGT94AV1 in B. monnieri enhanced the accumulation of jujubogenin-derived bacosides, while its knockdown reduced their levels. Further, transcriptome analysis has identified BmMYB14 co-expressing with UGT94AV1 and the previously characterized UGT79A18. Overexpression of BmMYB14 significantly upregulated UGT79A18 and UGT94AV1, whereas silencing of BmMYB14 markedly reduced their transcript levels. The expressions of UGT94AV1 and UGT79A18 in BmMYB14 OE and KD lines were consistent with enhanced accumulation of bacosides in OE lines and reduced in KD lines. Yeast one-hybrid and dual-luciferase assays using the promoter regions of UGT94AV1 and UGT79A18 further demonstrate that BmMYB14 transcriptionally regulates UGT79A18 and UGT94AV1, and hence contributes to the dammarane-type triterpene biosynthesis in Bacopa monnieri.