Proposed to be involved in the biosynthesis of pterocarpan phytoalexins, specifically glyceollins. Can act as a prenyltransferase towards glycinol which is the direct precursor of glyceollins. Seems to be specific for prenylation at C-4 thus producing glyceollin I. (6aS,11aS)-3,6a,9-trihydroxypterocarpan + dimethylallyl diphosphate = (6aS,11aS)-2-dimethylallyl-3,6a,9-trihydroxypterocarpan + diphosphate (6aS,11aS)-3,6a,9-trihydroxypterocarpan + dimethylallyl diphosphate = (6aS,11aS)-4-dimethylallyl-3,6a,9-trihydroxypterocarpan + diphosphate Magnesium or manganese or cobalt at a lesser extent. Phytoalexin biosynthesis; pterocarpan phytoalexin biosynthesis. Upon treatment with yeast extract. Belongs to the UbiA prenyltransferase family.