Abstract

Stevia rebaudiana Bertoni, a member of the Asteraceae family, is recognized for its sweetened leaves, which are remarkably sweeter than sucrose by 200–300 times. This astounding property is because of steviol glycosides (SGs), a class of diterpenoid secondary metabolites that primarily consist of stevioside and rebaudioside A. These compounds are formed through a specific SG biosynthetic pathway that contains several key genes. In the present work, gene expression profiling of 15 core genes of SG biosynthetic pathway, along with metabolite analysis, was conducted in three groups of S. rebaudiana plants: In vitro regenerated non-transformed plantlets (NP), in vitro regenerated transformed plantlets (TP) via hairy root cultures using Rhizobium rhizogenes mediated transformation, and control plants (CP). Quantitative real-time polymerase chain reaction results showed that in NP and TP there was upregulation of 13 genes. Both NP and TP showed downregulated SrDXR and SrCDPS in comparison to CP, whereas SrUGT74G1 had higher expression in NP than TP. High-performance liquid chromatography chromatographic studies on SGs showed that stevioside content followed the order TP > NP > CP. These findings demonstrate that transformation enhances SG biosynthesis and support the use of genetically modified S. rebaudiana lines for increased natural sweetener production. Further studies are warranted to elucidate regulatory mechanisms and optimize metabolic engineering approaches.

Key words: Stevia rebaudiana, Secondary metabolites, Steviol Glycosides pathway, gene expression, qRT-PCR, HPLC