Abstract
Glycyrrhizin is a saponin accumulated in the underground parts of licorice, Glycyrrhiza plants. Glycyrrhizin is used as a natural sweetener and medicine in the world. Recently, we identified the biosynthetic genes, CYP88D6 [Seki H. et al. PNAS (2008)] and a CYP72A, from G. uralensis. Moreover, our recombinant yeast produced the aglycone, glycyrrhetinic acid. Genus Glycyrrhiza also contains glycyrrhizin non-producing species, and these species produce saponins similar to glycyrrhizin. In this study, we have investigated the molecular mechanisms responsible for the structural diversity of saponins in the Glycyrrhiza species by comparative analysis of the P450 gene homologs.
We cloned CYP88D6 homologous genes from other Glycyrrhiza species by PCR. The phylogenetic tree of those deduced amino acid sequences showed the homologues were divided into two groups, glycyrrhizin producing and non-producing species. The result of functional evaluation of those genes using yeast expression system suggested that the catalytic properties of the CYP88D6 homologues are responsible for the glycyrrhizin production and the chemical diversity of saponins in Glycyrrhiza species.
