Unlocking saponin biosynthesis in soapwort
Seohyun Jo, Amr El‐Demerdash, Charlotte Owen, Vikas Srivastava, Dewei Wu, Shingo Kikuchi, James Reed, Hannah Hodgson, Alex Harkess, Shengqiang Shu, Christopher Plott, Jerry Jenkins, Melissa Williams, LoriBeth Boston, Elia Lacchini, Tongtong Qu, Alain Goossens, Jane Grimwood, Jeremy Schmutz, Jim Leebens‐Mack, Anne Osbourn
Abstract
Soapwort (Saponaria officinalis) is a flowering plant from the Caryophyllaceae family with a long history of human use as a traditional source of soap. Its detergent properties are because of the production of polar compounds (saponins), of which the oleanane-based triterpenoid saponins, saponariosides A and B, are the major components. Soapwort saponins have anticancer properties and are also of interest as endosomal escape enhancers for targeted tumor therapies. Intriguingly, these saponins share common structural features with the vaccine adjuvant QS-21 and, thus, represent a potential alternative supply of saponin adjuvant precursors. Here, we sequence the S. officinalis genome and, through genome mining and combinatorial expression, identify 14 enzymes that complete the biosynthetic pathway to saponarioside B. These enzymes include a noncanonical cytosolic GH1 (glycoside hydrolase family 1) transglycosidase required for the addition of D-quinovose. Our results open avenues for accessing and engineering natural and new-to-nature pharmaceuticals, drug delivery agents and potential immunostimulants.