Upregulation of phytosterol and triterpene biosynthesis in Centella asiatica hairy roots overexpressed ginseng farnesyl diphosphate synthase

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Abstract
Farnesyl diphosphate synthase (FPS) plays an essential role in organ development in plants. However, FPS has not previously been identified as a key regulatory enzyme in triterpene biosynthesis. To elucidate the functions of FPS in triterpene biosynthesis, C. asiatica was transformed with a construct harboring Panax ginseng FPS (PgFPS)-encoding cDNA coupled to the cauliflower mosaic virus 35S promoter. Higher levels of CaDDS (C. asiatica dammarenediol synthase) and CaCYS (C. asiatica cycloartenol synthase) mRNA were detected in all hairy root lines overexpressing when compared with the controls. However, no differences were detected in any expression of the CaSQS (C. asiatica squalene synthase) gene. In particular, the upregulation of CaDDS transcripts suggests that FPS may result in alterations in triterpene biosynthesis capacity. Squalene contents in the T17, T24, and T27 lines were increased to 1.1-, 1.3- and 1.5-fold those in the controls, respectively. The total sterol contents in the T24 line were approximately three times higher than those of the controls. Therefore, these results indicated that FPS performs a regulatory function in phytosterol biosynthesis. To evaluate the contribution of FPS to triterpene biosynthesis, we applied methyl jasmonate as an elicitor of hairy roots expressing PgFPS. The results of HPLC analysis revealed that the content of madecassoside and asiaticoside in the T24 line was transiently increased by 1.15-fold after 14 days of MJ treatment. This result may indicate that FPS performs a role not only in phytosterol regulation, but also in triterpene biosynthesis.

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