Analysis of soyasaponin content and biosynthesis-related gene expression in young pea (Pisum sativum L.) sprouts

In legumes, soyasaponins, one of triterpenoid saponins, are major components of secondary metabolites with a more diverse array of bioactive chemicals. Although the biosynthetic pathway of soyasaponins has been largely studied in soybean, the study on the soyasaponin contents and biosynthesis-related gene expression in pea (Pisum sativum L.) is poorly understood. Here, we found the accumulation of only soyasaponin Bb component in the sprouts of two Korean domestic pea cultivars (Dachung and Sachul). This pattern was consistent with our observation that increased expression of PsUGT73P2 and PsUGT91H4 genes, but not PsCYP72A69, could be responsible for biosynthesis of only soyasaponin Bb in pea by examining their gene expression. However, gradual accumulation of soyasaponin Bb at developmental stages was not consistent with the expression of PsUGT73P2 and PsUGT91H4, suggesting that the changes of their protein activities may affect the accumulation patterns of soyasaponin Bb. We also revealed that the increased expression levels of PsUGT73P2 and PsUGT91H4 during light to dark transition led to increase of soyasaponin Bb contents. Collectively, our results provided a molecular basis of metabolic engineering for enhancing useful soyasaponin Bb metabolites in Korean domestic pea cultivars.