The Effects of Silveroxide on mRNA Level of Key Genes Involved In the Biosynthesis of Rebaudioside-A in Stevia Rebaudiana

Abstract

Stevia rebaudiana bertoni is a plant with sweetening properties. This medicinal plant is perennial and from Asteraceae family. Its leaves contain glycoside compounds of a sugar part and non-sugar sectors. One of the glycosides compounds is Rebaudioside¬A which has a greater importance in market. Several key regulating genes including copalyl diphosphate synthase (CPPS) (AF034545.1), geranylgeranyl diphosphate synthase (GGDPS) (DQ432013.3), (E)-4-hydroxy-3-methylbut-2-enyl diphosphate synthase (HDS) (FJ755689.1), UDP glucosyltranserase 85C2(UGT85C2)(AY345978.1), UDPglucosyltranserase–74G1 (UGT74G1) (AY345982.1) and UDP glucosyltranserase–76G1 (UGT76G1) (KC631816.1) are involved in the biosynthesis Rebaudioside A. This experiment was conducted to evaluate the effect of silver oxide Ag2O on the mRNA level of these genes in the stevia rebaudiana. The experiments repeated 3 times and with concentrations of 50, 100 and 200 µM. Increasing concentrations of 50 micromoles of silver oxide up to 100 micromoles leads to an increase in the expression levels of all the studied genes. Also according to the expression profile of these genes and the results of HPLC there is a significant increase on the expression level of the genes and production of Rebaudioside¬A under Ag2O treatment. In general, it was found that increasing the concentration of Ag2O can lead to an increase in the level of mRNA for the chosen genes. On the other hand, the low expression of the genes studied under control conditions (No Treatment), compared to the treatment with Ag2O, revealed that the treatment can lead to higher sweetener glycoside components in the Stevia leaves. The physiological assay showed that Ag2O treatment in concentrations of 100 and 200 µM have more positive effect on chlorophyll, protein, carbohydrates and carotenoids in Stevia.