Regulation of ginsenoside and phytosterol biosynthesis by RNA interferences of squalene epoxidase gene in Panax ginseng.

Squalene epoxidase catalyzes the first oxygenation step in phytosterol and triterpenoid saponin biosynthesis and is suggested to represent one of the rate-limiting enzymes in this pathway. Here, we investigated the roles of two squalene epoxidase genes (PgSQE1 and PgSQE2) in triterpene and phytosterol biosynthesis in Panax ginseng. PgSQE1 and PgSQE2 encoded deduced proteins of 537 and 545 amino acids, respectively. Amino acid sequences deduced from PgSQE1 and PgSQE2 share 83% homology, but the N-terminal regions (first 60 amino acids) are highly different. PgSQE1 mRNA abundantly accumulated in all organs. PgSQE2 was only weakly expressed and preferentially in petioles and flower buds. Methyl jasmonate (MeJA) treatment enhanced the accumulation of PgSQE1 mRNA in roots, but rather suppressed expression of PgSQE2. Precursor (squalene) treatment coordinately upregulated the expression of both PgSQE1 and PgSQE2. In situ hybridization analysis established that both PgSQE1 and PgSQE2 mRNAs accumulated preferentially in vascular bundle tissue and resin ducts of petioles. RNA interference of PgSQE1 in transgenic P. ginseng completely suppressed PgSQE1 transcription. Concomitantly, the interference of PgSQE1 resulted in reduction of ginsenoside production. Interestingly, silencing of PgSQE1 in RNAi roots strongly upregulated PgSQE2 and PNX (cycloartenol synthase) and resulted in enhanced phytosterol accumulation. These results indicate that expression of PgSQE1 and PgSQE2 were regulated in a different manner, and that PgSQE1 will regulate ginsenoside biosynthesis, but not that of phytosterols in P. ginseng.

Han JY ，In JG ，Kwon YS ，Choi YE ... -  《-》

Enhanced triterpene and phytosterol biosynthesis in Panax ginseng overexpressing squalene synthase gene.

Lee MH ，Jeong JH ，Seo JW ，Shin CG ，Kim YS ，In JG ，Yang DC ，Yi JS ，Choi YE ... -  《PLANT AND CELL PHYSIOLOGY》

[Development of the devices for synthetic biology of triterpene saponins at an early stage: cloning and expression profiling of squalene epoxidase genes in panax notoginseng].

Niu YY ，Zhu XX ，Luo HM ，Sun C ，Huang LF ，Chen SL ... -  《-》

PgLOX6 encoding a lipoxygenase contributes to jasmonic acid biosynthesis and ginsenoside production in Panax ginseng.

Ginsenosides, the valuable pharmaceutical compounds in Panax ginseng, are triterpene saponins that occur mainly in ginseng plants. It was shown that in vitro treatment with the phytohormone jasmonic acid (JA) is able to increase ginsenoside production in ginseng plants. To understand the molecular link between JA biosynthesis and ginsenoside biosynthesis, we identified a JA biosynthetic 13-lipoxygenase gene (PgLOX6) in P. ginseng that promotes ginsenoside production. The expression of PgLOX6 was high in vascular bundles, which corresponds with expression of ginsenoside biosynthetic genes. Consistent with the role of PgLOX6 in synthesizing JA and promoting ginsenoside synthesis, transgenic plants overexpressing PgLOX6 in Arabidopsis had increased amounts of JA and methyl jasmonate (MJ), increased expression of triterpene biosynthetic genes such as squalene synthase (AtSS1) and squalene epoxidase (AtSE1), and increased squalene content. Moreover, transgenic ginseng roots overexpressing PgLOX6 had around 1.4-fold increased ginsenoside content and upregulation of ginsenoside biosynthesis-related genes including PgSS1, PgSE1, and dammarenediol synthase (PgDDS), which is similar to that of treatment with MJ. However, MJ treatment of transgenic ginseng significantly enhanced JA and MJ, associated with a 2.8-fold increase of ginsenoside content compared with the non-treated, non-transgenic control plant, which was 1.4 times higher than the MJ treatment effect on non-transgenic plants. These results demonstrate that PgLOX6 is responsible for the biosynthesis of JA and promotion of the production of triterpenoid saponin through up-regulating the expression of ginsenoside biosynthetic genes. This work provides insight into the role of JA in biosynthesizing secondary metabolites and provides a molecular tool for increasing ginsenoside production.

Rahimi S ，Kim YJ ，Sukweenadhi J ，Zhang D ，Yang DC ... -  《-》

Expression and RNA interference-induced silencing of the dammarenediol synthase gene in Panax ginseng.

Han JY ，Kwon YS ，Yang DC ，Jung YR ，Choi YE ... -  《PLANT AND CELL PHYSIOLOGY》