Identification of an inducible glucosyltransferase from Phytolacca americana L. cells that are capable of glucosylating capsaicin

Cell suspension cultures of Phytolacca americana L. (pokeweed) are capable of glycosylating capsaicinoids that have several biomedical applications. To identify the capsaicinoid glucosyltransferase involved in this biotransformation, we isolated three full-length cDNAs (PaGTs) encoding homologs of plant secondary product glycosyltransferases from cultured cells of P. americana L. These glycosyltransferase cDNAs were heterologously expressed in Escherichia coli cells and the expressed products were functionally characterized. Although all of these glycosyltransferases displayed broad glucosyl-acceptor specificities toward phenolics, capsaicinoid glucosyltransferase activity was found only for one of the cloned enzymes, PaGT3. Phylogenetic analysis showed that PaGT3 is the most closely related to betanidin 5-O- glucosyltransferase from Dorotheanthus bellidiformis, and in fact, it displayed a weak betanidin 5-O-glucosyltransferase activity. Transcription analyses showed that the expression of PaGT3 in P. americana L. was strongly induced by exposure of the cells to capsaicin (0.65mM). These results show that PaGT3 should be, at least in part, responsible for the capsaicinoid glucosyltransferase activity of this plant.