Identification and Characterization of Two Bibenzyl Glycosyltransferases from the Liverwort .

Liverworts are rich in bibenzyls and related -glycosides, which show antioxidant activity. However, glycosyltransferases that catalyze the glycosylation of bibenzyls have not yet been characterized. Here, we identified two bibenzyl UDP-glucosyltransferases named UGT737B1 and UGT741A1 from the model liverwort . The in vitro enzymatic assay revealed that UGT741A1 specifically accepted the bibenzyl lunularin as substrate. UGT737B1 could accept bibenzyls, dihydrochalcone and phenylpropanoids as substrates, and could convert phloretin to phloretin-4--glucoside and phloridzin, which showed inhibitory activity against tyrosinase and antioxidant activity. The results of sugar donor selectivity showed that UGT737B1 and UGT741A1 could only accept UDP-glucose as a substrate. The expression levels of these UGTs were considerably increased after UV irradiation, which generally caused oxidative damage. This result indicates that UGT737B1 and UGT741A1 may play a role in plant stress adaption. Subcellular localization indicates that UGT737B1 and UGT741A1 were expressed in the cytoplasm and nucleus. These enzymes should provide candidate genes for the synthesis of bioactive bibenzyl -glucosides and the improvement of plant antioxidant capacity.