## 1 Introduction  
_Stevia rebaudiana_ is a perennial bushy shrub that belongs to the Asteraceae family. Over 200 years ago, the indigenous people of South America used its leaves to sweeten beverages and chewed them for their sweet taste. The stevia plant was first officially recorded in 1899 as _Eupatorium rebaudianum_ by the scientist [PERSON] in the Amambay region, in the northeast of Paraguay (South America) [1]. Later, in 1905 it was renamed _Stevia rebaudiana_ after the chemist [PERSON] [2]. It is also known as the \"sweet herb of Paraguay\", honey leaf, candy leaf, and sweet herb [3]. With its increasing popularity, in 1970, for the first-time stevia plant extract was commercially adopted as a natural sweetener by Japan. Currently, stevia is commercially available in China, Brazil, Kenya, the United Kingdom, and several regions in Asia (India, Indonesia Korea, Malaysia, Philippines, and Thailand). The stevia plant contains secondary metabolite steviol glycosides (SvGls), which are mostly synthesized in leaves and in small amounts in the stem [4]. Steviol glycosides are chemical compounds derived from plant parts and are known for their unique property of sweetness. SvGls have become an important third-generation natural zero-calorie healthy sugar source with additional benefits in controlling several chronic diseases (obesity, diabetes, cardiac blockage, and hypertension) [1]. SGs are not absorbed and metabolized in the human body, making them a low-calorie sweetener [5]. Of more than 230 stevia species known, _Stevia rebaudiana_ (Bertoni) is the most popular because of its sweetness [6]. Apart from _S. rebaudiana_, SvGls have been found in three other species: _Stevia plehophylla, Rubus suavissimus_, and _Angelica keiskei_. However, these plant species are of less economic importance as they have a low production rate of SvGls compared to _S. rebaudiana_[7]. SvGls show wide diversity, and there are approximately forty SvGls known so far. SvGls along with some other secondary metabolites, for example, coumarins, flavonoids (19.93 mg/g), phenols (24.01 mg/g), and tannins (56.7 mg/g), and some essential oils have given _Stevia rebaudiana_ importance in various medicines and food additives [8]. Twelve SvGls are more popular, based on the number of sugar bases attached to the aglycone core [9]. Generally, the SvGls with more sugar bases (Reb M, Reb D, Reb A) are found to be sweeter than those with fewer sugar bases (stevioside) [10]. Stevioside is the most abundant SvGls found in stevia leaves (5-10%) followed by Reb A (2-4%) and Reb M (<0.1%). The safety approval of the use of stevia extract from the US Food and Drug Administration (USFDA) in 2008 and European Food Safety Agency (EFSA) in 2011, led to an accelerated interest in stevia-derived compounds. Stevioside, Reb A, and high-purity Reb M (\(\geq\)95%) derived from stevia are recognized as safe for human consumption (GRAS) [11]. High-grade stevioside and rebaudiosides are now used in many parts of Asia, America, and Europe. Despite such high global market expansion, the production of high-quality stevia is problematic and insufficient to meet the current demand [12]. Since the very beginning, the aim of cultivators and breeders was the genetic improvement and development of varieties with higher life and yield of SvGls and increased abiotic and biotic stress resistance compared to other commonly found stevia cultivars. However, research is ongoing to find novel stevia-derived compounds and also to identify the key genes regulating the synthesis of desired SvGls with a sweeter taste preferable for food and pharmaceutical industries. The main aim of this review is to encapsulate all the recent conventional and biotechnological advances made so far to enhance the SvGls production. Earlier studies have described the biosynthesis of SvGls and methods used to stimulate the production of SvGls in _Stevia rebaudiana_[7; 13]. However, they fail to cover the current detailed information on the newly identified regulatory enzymes involved in the biosynthesis of SvGls.