Discovery of plant chemical defence mediated by a two-component system involving β-glucosidase in Panax species

Abstract

Plants usually produce defence metabolites in non-active forms to minimize the risk of harm to themselves and spatiotemporally activate these defence metabolites upon pathogen attack. This so-called two-component system plays a decisive role in the chemical defence of various plants. Here, we discovered that Panax notoginseng, a valuable medicinal plant, has evolved a two-component chemical defence system composed of a chloroplast-localized β-glucosidase, denominated PnGH1, and its substrates 20(S)-protopanaxadiol ginsenosides. The β-glucosidase and its substrates are spatially separated in cells under physiological conditions, and ginsenoside hydrolysis is therefore activated only upon chloroplast disruption, which is caused by the induced exoenzymes of pathogenic fungi upon exposure to plant leaves. This activation of PnGH1-mediated hydrolysis results in the production of a series of less-polar ginsenosides by selective hydrolysis of an outer glucose at the C-3 site, with a broader spectrum and more potent antifungal activity in vitro and in vivo than the precursor molecules. Furthermore, such β-glucosidase-mediated hydrolysis upon fungal infection was also found in the congeneric species P. quinquefolium and P. ginseng. Our findings reveal a two-component chemical defence system in Panax species and offer insights for developing botanical pesticides for disease management in Panax species.

Rationally Engineered Novel Glycosyltransferase UGT74DD1 from Siraitia grosvenorii Catalyzes the Generation of the Sweetener Mogroside III

“…Glycosylation is pivotal to the synthesis of complex, structurally diverse glycosides, enhancing the bioactivity and bioavailability of aglycones. , Triterpene saponins are structurally diverse natural products with different skeletons that are modified by multiple sugar moieties. − In plants, the glycosylation of triterpene saponins can be catalyzed by glycosyltransferases (GTs), offering a highly efficient, regio- and stereospecific approach for the formation of glycosidic bonds. For example, GTs in ginseng play important roles in the formation of diverse ginsenosides. , Triterpene glycosylation is typically a polyglycosylation process, often involving branched glycosylation following primary glycosylation .…”