The unprecedented diversity of UGT94-family UDP-glycosyltransferases in Panax plants and their contribution to ginsenoside biosynthesis

More than 150 ginsenosides have been isolated and identified from Panax plants. Ginsenosides with different glycosylation degrees have demonstrated different chemical properties and bioactivity. In this study, we systematically cloned and characterized 46 UGT94 family UDP-glycosyltransferases (UGT94s) from a mixed Panax ginseng/callus cDNA sample with high amino acid identity. These UGT94s were found to catalyze sugar chain elongation at C3-O-Glc and/or C20-O-Glc of protopanaxadiol (PPD)-type, C20-O-Glc or C6-O-Glc of protopanaxatriol (PPT)-type or both C3-O-Glc of PPD-type and C6-O-Glc of PPT-type or C20-O-Glc of PPD-type and PPT-type ginsenosides with different efficiencies. We also cloned 26 and 51 UGT94s from individual P. ginseng and P. notoginseng plants, respectively; our characterization results suggest that there is a group of UGT94s with high amino acid identity but diverse functions or catalyzing activities even within individual plants. These UGT94s were classified into three clades of the phylogenetic tree and consistent with their catalytic function. Based on these UGT94s, we elucidated the biosynthetic pathway of a group of ginsenosides. Our present results reveal a series of UGTs involved in second sugar chain elongation of saponins in Panax plants, and provide a scientific basis for understanding the diverse evolution mechanisms of UGT94s among plants.