Genome-Wide Identification of UGT Gene Family and Functional Analysis of PgUGT29 in Platycodon grandiflorus

Uridine diphosphate glycosyltransferase (UGT) is a core protein for glycosylation of plant natural products and other small molecules. Although many studies on functional identification of UGTs are now available, analysis of UGTs in <i>Platycodon grandiflorus</i> is still relatively scarce. We identified 107 PgUGTs genome-wide from <i>P. grandiflorus</i> and investigated their phylogenetic relationships, chromosomal localisation, collinearity, cis-regulatory elements, motifs, domains, and gene structures. PgUGT29 and PgUGT72 were two putative glycosyltransferases for platycodins biosynthesis in <i>P. grandiflorus</i> according to our previous study and bioinfornatical analyses. In vitro enzyme activity showed that PgUGT29 can catalyse the glycosylation of the C3 position of Platycodin D (PD) to generate Platycodin D3 (PD3), while candidate enzyme PgUGT72 does not function as a glycosyltransferase. Molecular docking indicated that T145, D392, Q393, and N396 may be the crucial residues for PgUGT29 to catalyse the generation of PD3 from UDP-Glc and PD. In this study, we identified and cloned PgUGT29, elucidated its catalytic function in converting PD to PD3, and predicted key residues critical for its enzymatic activity. These findings provide a theoretical foundation and technical framework for future targeted metabolic engineering and directional regulation of medicinal components in <i>Platycodon grandiflorus</i>.