Effect of Silver Nanoparticle Treatment on the Expression of Key Genes Involved in Glycosides Biosynthetic Pathway in Stevia rebaudiana B. Plant

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.