Identification and RNAi-based gene silencing of a novel UDP-glycosyltransferase from Panax quinquefolius

Panax quinquefolius (P. quinquefolius) has been used as medicine for thousands of years in Asia. Ginsenosides are major pharmacological active components extracted from P. quinquefolius. Glycosylation is the last and the most important step in the ginsenosides biosynthesis pathway, however, the function of glycosyltransferase has been poorly understood in the biosynthesis pathway of ginsenosides. In this study, we cloned and identified a novel UDP-glycosyltransferase gene from P. quinquefolius (Pq-PPT-6,20-O-UGT1) for the first time. The high similarity of amino acid sequence indicated a close evolutionary relationship and analogous function among PPT-6,20-O-UGT1 and several UDP-glycosyltransferases in P. quinquefolius or Panax ginseng. In vitro enzymatic assay confirmed that Pq-PPT-6,20-O-UGT1 could glycosylate the C20-OH of PPT and the C6-OH of ginsenoside F1 (F1), so that ginsenoside F1 and ginsenosides Rg1 (Rg1) were produced, respectively. Moreover, we established RNA interference (RNAi) transgenic root lines of Pq-PPT-6,20-O-UGT1. The expression levels of dammarenediol synthase, protopanaxadiol synthase and protopanaxatriol were up-regulated in RNAi lines. These results illustrated that Pq-PPT-6,20-O-UGT1 was a key enzyme for the synthesis of Rg1 and F1.