Stevia rebaudiana extract is globally approved as a low-calorie sweetener. Increasing glycosides content using biotechnological methods is particularly important. In this study, stevia plant was treated with silver nanoparticles at various concentrations (0, 10, 20, and 40 mM). Subsequently, the transcription of key gene levels in the biosynthesis of rebaudioside and stevioside glycosides, including UGT85C2 (UDP-glycosyltransferases), KAH (Kaurenoic acid-13 hydroxylase), UGT74G1, and UGT76G1 was measured using real time PCR assays. The HPLC was used to evaluate the glycosides content. UGT85C2 demonstrated the highest transcriptional level changes in plants treated with silver nanoparticles. The plants treated with silver nanoparticles at concentration of 10 and 20 mM showed a lower gene expression than the control plant, but plant treated with silver nanoparticles at 40 mM concentration showed significantly higher gene expression than the control samples. The results suggested that the treatment with AgNPs at 40 mM leads to similar positive effects on the transcription of all genes. HPLC results also revealed that the plants treated with 40 mM nanoparticles contains a higher glycosides content comparing to the control sample. Thus, the present experiment suggests that silver nanoparticles can act as a strong amplifier of the transcriptional trigger for steviol glycoside biosynthesis pathway genes which have the potential to control the production of steviol glycosides positively.

中文翻译：

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银纳米颗粒处理对甜叶菊甜菊糖苷生物合成途径关键基因表达的影响

甜叶菊提取物被全球认可为低热量甜味剂。使用生物技术方法提高糖苷含量尤为重要。在这项研究中，甜叶菊植物用各种浓度（0、10、20和40 mM）的银纳米颗粒处理。随后，利用实时PCR分析法测定了莱鲍迪甙和甜菊糖苷的生物合成中的关键基因水平的转录，包括UGT85C2（UDP-糖基转移酶），KAH（Kaurenoic acid-13羟化酶），UGT74G1和UGT76G1。HPLC用于评估糖苷含量。UGT85C2在用银纳米颗粒处理的植物中显示出最高的转录水平变化。用银纳米颗粒以10和20 mM的浓度处理的植物显示出比对照植物低的基因表达，但是用浓度为40 mM的银纳米颗粒处理的植物显示出明显高于对照样品的基因表达。结果表明，以40 mM的AgNPs处理对所有基因的转录产生相似的积极影响。HPLC结果还显示，与对照样品相比，用40mM纳米颗粒处理的植物含有更高的糖苷含量。因此，本实验表明银纳米颗粒可以作为甜菊醇糖苷生物合成途径基因的转录触发的强大扩增子，该基因具有积极控制甜菊糖苷生产的潜力。结果表明，以40 mM的AgNPs处理对所有基因的转录产生相似的积极影响。HPLC结果还显示，与对照样品相比，用40mM纳米颗粒处理的植物含有更高的糖苷含量。因此，本实验表明银纳米颗粒可以作为甜菊醇糖苷生物合成途径基因的转录触发的强大扩增子，该基因具有积极控制甜菊糖苷生产的潜力。结果表明，以40 mM的AgNPs处理对所有基因的转录产生相似的积极影响。HPLC结果还显示，与对照样品相比，用40mM纳米颗粒处理的植物含有更高的糖苷含量。因此，本实验表明银纳米颗粒可以作为甜菊醇糖苷生物合成途径基因的转录触发的强大扩增子，该基因具有积极控制甜菊糖苷生产的潜力。