## 1 Introduction
Several attempts have been made to decode their distinct metabolic profiles through high throughput metabolic fingerprinting methods including nuclear magnetic resonance (NMR), gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), and capillary electrophoresis-mass spectrometry (CE-MS), and so-called metabolomics [19]. Metabolic engineering is an appropriate system to either enhance or manipulate the synthesis of terpen in plant species that naturally produce them, or to integrate terpene biosynthetic pathways into certain plants [20]. A number of attempts have been made over the last decade to engineer the production of monoterpenoid and sesquiterpenoid compounds in various plant species and tissues. Implementing modern analytical techniques is the best way to improve the qualitative and quantitative aspects of terpenes and terpenoids in plants and other products [21]. All plants produce a variety of terpenoid compounds that serve as phytohormones and anti-oxidants, or have other functions. Hundreds of distinct terpenoids are synthesized by different plant lineages, with the overall number of such advanced plant terpenoids estimated to be in the thousands [22]. A clear understanding of a plant's chemical composition enables a more accurate assessment of its medicinal potential. Modern chemistry can unravel the primary metabolic functions of plants, including cell division, development, respiration, storage, and reproduction. It helps improve our understanding of process components, such as glycolysis, the cancer or cycles of citric acid, and photosynthesis [23]. Small molecules, such as sugars, amino acids, proteins, nucleic acids, and polysaccharides, are examples of primary metabolites [24; 25]. Secondary plant metabolites are a diverse group of chemical compounds synthesized by the plant cell through metabolic pathways derived from primary metabolic pathways [26]. By the mid-twentieth century, advancements in analytical techniques such as GC-MS, LC-MS, CE-MS, and NMR enabled the recovery of an increasing number of these molecules, providing a basis for the development of phytochemistry. Secondary plant metabolites are classified into specific categories: phenolics, alkaloids, saponins, terpenes, lipids, and carbohydrates [27]. Terpenes are the major and most varied category of secondary metabolites found in plants. Green plants, especially flowering plants, have an extraordinarily high number of terpenoids compared to other living organisms [22]. Isoprene units in the molecules, mono-terpenoids (C10), sesquiterpenoids(C15), triterpenoids (C20), and triterpenoids (C30) are considered secondary metabolites. Many terpenoids are commercially interesting because of their use as flavors and fragrances in foods and cosme (e.g., menthol, nootkatone, and sclaerol) or because they are important for the quality of agricultural products, for example, with the flavor of fruits and the fragrance of flowers (e.g., linalool) [28]. In addition, terpenoids have medicinal properties including anti-carcinogenic (e.g., taxol and perilla alcohol), antimalarial (e.g., artemisinin), anti-ulcer, hepaticidal, antimicrobial, and diuretic (e.g., glycyrrhizin) activities [29]. Terpenoids have also been shown to be of ecological significance. Compounds, such as the bitter triterpenoid cucurbitacians and the pungent diterpenoid polygonal, have been shown to be involved in insect resistance [30]. Other terpenoid substances are active in plant interactions, plant-microorganism interactions, and plant-arthropod herbivore interactions (for example, spider mite feeding induces (E, E)-a-farnesene in cucumber) [31]. In this review, we provide an overview of the recent developments in relation to different biosynthetic and regulatory aspects of monoterenoid and sesquiterpenoid metabolism in plants. Moreover, we report on the remarkable improvement in metabolic engineering for advanced terpenoid production in various platforms.