Engineering of triterpene metabolism and overexpression of the lignin biosynthesis gene PAL promotes ginsenoside Rg 3 accumulation in ginseng plant chassis.

The ginsenoside Rg3 found in Panax species has extensive pharmacological properties, in particular anti-cancer effects. However, its natural yield in Panax plants is limited. Here, we report a multi-modular strategy to improve yields of Rg3 in a Panax ginseng chassis, combining engineering of triterpene metabolism and overexpression of a lignin biosynthesis gene, phenylalanine ammonia lyase (PAL). We first performed semi-rational design and site mutagenesis to improve the enzymatic efficiency of Pq3-O-UGT2, a glycosyltransferase that directly catalyzes the biosynthesis of Rg3 from Rh2 . Next, we used CRISPR/Cas9 gene editing to knock down the branch pathway of protopanaxatriol-type ginsenoside biosynthesis to enhance the metabolic flux of the protopanaxadiol-type ginsenoside Rg3 . Overexpression of PAL accelerated the formation of the xylem structure, significantly improving ginsenoside Rg3 accumulation (to 6.19-fold higher than in the control). We combined overexpression of the ginsenoside aglycon synthetic genes squalene epoxidase, Pq3-O-UGT2, and PAL with CRISPR/Cas9-based knockdown of CYP716A53v2 to improve ginsenoside Rg3 accumulation. Finally, we produced ginsenoside Rg3 at a yield of 83.6 mg/L in a shake flask (7.0 mg/g dry weight, 21.12-fold higher than with wild-type cultures). The high-production system established in this study could be a potential platform to produce the ginsenoside Rg3 commercially for pharmaceutical use. This article is protected by copyright. All rights reserved.