Abstract
Pterocarpans are derivatives of isoflavonoids, found in many species of the family Fabaceae. Sophora flavescens Aiton is a promising traditional Asian medicinal plant. Plant cell suspension cultures represent an excellent source for the production of valuable secondary metabolites. Herein, we found that methyl jasmonate (MJ) elicited the activation of pterocarpan biosynthetic genes in cell suspension cultures of S. flavescens and enhanced the accumulation of pterocarpans, producing mainly trifolirhizin, trifolirhizin malonate, and maackiain. MJ application stimulated the expression of structural genes (PAL, C4H, 4CL, CHS, CHR, CHI, IFS, I3’H, and IFR) of the pterocarpan biosynthetic pathway. In addition, the co-treatment of MJ and methyl-β-cyclodextrin (MeβCD) as a solubilizer exhibited a synergistic effect on the activation of the pterocarpan biosynthetic genes. The maximum level of total pterocarpan production (37.2 mg/g dry weight (DW)) was obtained on day 17 after the application of 50 μM MJ on cells. We also found that the combined treatment of cells for seven days with MJ and MeβCD synergistically induced the pterocarpan production (trifolirhizin, trifolirhizin malonate, and maackiain) in the cells (58 mg/g DW) and culture medium (222.7 mg/L). Noteworthy, the co-treatment only stimulated the elevated extracellular production of maackiain in the culture medium, indicating its extracellular secretion; however, its glycosides (trifolirhizin and trifolirhizin malonate) were not detected in any significant amounts in the culture medium. This work provides new strategies for the pterocarpan production in plant cell suspension cultures, and shows MeβCD to be an effective solubilizer for the extracellular production of maackiain in the cell cultures of S. flavescens.
Highlights
We demonstrate that the application of methyl jasmonate (MJ) alone or together with MeβCD in the cell cultures of S. flavescens has a significant and synergistic effect on the expression of structural genes involved in pterocarpan biosynthesis, thereby leading to an enhanced production of pterocarpans, such as maackiain, trifolirhizin, and trifolirhizin malonate
We further report that combined treatment with MJ and MeβCD synergistically enhances the production of pterocarpans and preferentially induces the secretion of maackiain into the cell culture medium
The MJ-treated cells showed a similar growth pattern to that in the untreated cells, but they displayed about 38% reduction in cell biomass on day 12 compared to the untreated cells (Figure 2A)
Summary
Yamamoto et al [31,32,33] reported that callus cultures of S. favescens produced both prenylated flavanones (sophoraflavanone G and lehmannin) and pterocarpans [31,32,33] They reported that maackiain was not found in the fresh roots, but accumulated in the callus cultures of S. flavescens as the 6 -malonyl ester of its 3-O-glucoside (trifolirhizin malonate) [31]. We demonstrate that the application of MJ alone or together with MeβCD in the cell cultures of S. flavescens has a significant and synergistic effect on the expression of structural genes involved in pterocarpan biosynthesis, thereby leading to an enhanced production of pterocarpans, such as maackiain, trifolirhizin, and trifolirhizin malonate. We further report that combined treatment with MJ and MeβCD synergistically enhances the production of pterocarpans and preferentially induces the secretion of maackiain into the cell culture medium
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