A review on current conventional and biotechnical approaches to enhance biosynthesis of steviol glycosides in Stevia rebaudiana

Stevia rebaudiana Bertoni is commonly called stevia and mostly found in the north east regions of South America. It is an herbaceous and shrubby plant belonging to the Asteraceae family. Stevia is considered as a natural sweetener and a commercially important plant worldwide. The leaves of S. rebaudiana contain steviol glycosides (SGs) which are highly potent and non-caloric sweeteners. The sweetening property of S. rebaudiana is contributed to the presence of these high potency, calorie free steviol glycosides. SGs are considerably suitable for replacing sucrose and other artificial sweetening agents which are used in different industries and pharmaceuticals. SGs amount in the plant mostly varies from 8% to 10%, and the enhancement of SGs is always in demand. These glycosides have the potential to become healthier alternatives to other table sugars for having desirable taste and zero calories. SGs are almost 300 times sweeter than sucrose. Being used as alternative sugar intensifier the commercial value of this plant in biopharmaceutical, food and beverages industries and in international market is increasing day by day. SGs have made stevia an important part of the medicinal world as well as the food and beverage industry, but the limited production of plant material is not fulfilling the higher global market demand. Therefore, researchers are working worldwide to increase the production of important SGs through the intercession of different biotechnological approaches in S. rebaudiana. This review aims to describe the emerging biotechnological strategies and approaches to understand, stimulate and enhance biosynthesis of secondary metabolites in stevia. Conventional and biotechnological methods for the production of steviol glycosides have been briefly reviewed and discussed.