Abstract 1495 Plant UDP-glycosyltransferase in cardiotonic steroid biosynthesis

Cardiotonic steroids are a class of steroidal lactones widely found in plants.One lead example is digoxin, a US FDAapproved drug, isolated from foxglove (Digitalis lanata), for treating various heart conditions by inhibiting Na+/K+ ATPases.Despite their evident value and utility, the biosynthetic pathway of cardiotonic steroids remains elusive.Here, we investigate the glycosylation of the cardiotonic steroid scaffold, which is a key tailoring modification in accessing favourable pharmacokinetics.We performed RNA-seq and transcriptomic analysis of different tissues from D. lanata and generated a short list of UDP-glycosyltransferase (UGT) candidates.Each candidate was then transiently expressed in the leaves of Nicotiana benthamiana through Agrobacteriummediated DNA delivery.Cardiotonic steroid aglycone was concomitantly supplied as substrate.The leaves were then left to grow for 5 days before being harvested for compound extraction followed by LC-MS analysis.At present, our experiments have yet to yield the glycosylated product.One potential explanation is the insufficient presence of appropriate UDP-sugars in N. benthamiana.Moving forward, we plan to expand our candidate list to screen a broader range of UGTs with an exogenous supply of UDP-sugars.