Abstract
The cucurbitane-type triterpenoid glycosides, mogrosides, are the main active components of <em>Siraitia grosvenorii</em> fruit. Squalene and cucurbitadienol are among the intermediates of the biosynthetic pathway for the formation of cucurbitane-type triterpenoid backbones of mogrosides. It is recognized that the exogenous application of methyl jasmonate (MeJA) increases the accumulation of secondary metabolites in various plant species. Here, the effect of MeJA (50, 200, and 500 μM) on the accumulation of squalene and cucurbitadienol in the fruits of <em>S. grosvenorii</em> at 10, 20, and 30 days after flowering (DAF) was tested for the first time. Since mogroside II E is the main cucurbitane-type triterpenoid present at this time, its concentration was also determined. The results show that MeJA can indeed promote squalene and cucurbitadienol accumulation, the application of 500 μM MeJA at 30 DAF being optimal. The concentration of squalene and cucurbitadienol increased up to 0.43 and 4.71 μg/g dry weight (DW), respectively, both of which were 1.2-fold greater than that of the control. The content of mogroside II E increased by 15% over the untreated group. We subsequently analyzed the expression of key genes involved in the mogroside biosynthetic pathway, including the 3-hydroxy-3-methylglutaryl-coenzyme A reductase gene (<em>SgHMGR</em>), squalene synthetase gene (<em>SgSQS</em>), cucurbitadienol synthase gene (<em>SgCS</em>), and cytochrome P450 (<em>SgCYP450</em>) with quantitative real-time PCR. The results showed that transcriptional levels of these genes were upregulated following the treatment described above. Additionally, their responses in the presence of MeJA was related to the concentration and timing of MeJA treatment.
Highlights
Siraitia grosvenorii (Cucurbitaceae) is a perennial vine widely distributed in southern China in the Guangxi Province
We investigated the effect of different concentrations of methyl jasmonate (MeJA) on the squalene, cucurbitadienol, and mogroside II E concentrations of S. grosvenorii fruit at different stages of growth in order to find the optimal treatment for obtaining the greatest yield of these compounds
When squalene concentration was tested at 24 and 48 h following the application of three concentrations of MeJA (50, 200, and 500 μM) to S. grosvenorii fruit, in most cases, the results revealed enhanced squalene accumulation compared to that of the control
Summary
Siraitia grosvenorii (Cucurbitaceae) is a perennial vine widely distributed in southern China in the Guangxi Province. It is used as a zero-calorie sweetener, and historically, as a household remedy for colds, sore throats, and lung congestion [1,2]. Zhang et al / MeJA-induced responses in S. grosvenorii fruit. Mogrosides exhibit a wide range of pharmacological characteristics, e.g., anti-oxidant, immunomodulatory, liver-protecting, anti-fatigue and anti-microbial properties [4,5]. With an increased public awareness of healthy diets, S. grosvenorii fruit have increasingly been used in Chinese herbal medicine, dietary supplements, and soft drinks [4,6]
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