## 5 Synthetic Biology of Terpenoids  
Synthetic biology is defined as the 'design and building of novel biological components such as enzymes, genetic circuits, or restructuring of existing biological system'. Various monoterreponoids and sesquiterpenoids were synthesized over the last decade using engineered bacteria and yeast [93; 94]. The most well-known example of synthetic biology-based high value chemical production is artemisinin acid, the precursor of the antimalarial drug artemisinin, which was synthesized in engineered _Escherichia coli_ and baker's yeast, _Saccharomyces cerevisiae_, following ten years of optimization [95; 96]. Furthermore, a specialized limonene and perillyl alcohol manufacturing system was established in _E. coli_ by co-expression of heterologous, codon-optimized, _Staphylococcus aureus_, and _S. cerevisiae_ MVA pathway genes into _E. coli_ with _Abies grandis_ GPP synthase and _Mentha spicata_ limonene synthase genes. Optimum gene regulation and growing circumstance resulted in a 400 mg/L limonene titre [97]. However, alternative strategies in _E. coli_ focused on the MEP pathway genes DXS, and because IDI was overexpressed, the resulting strains provided a poor titre of 35.8 mg/L limonene [98]. Similarly, using _Yarrowia lipolytica_ yeast, sesquiterpenes (+)-nookatatone was synthesized by heterologous co-expressing genes such as valencene synthase, nootkatone synthase, and NADPH-cytochrome P450 reductase, resulting in 978.2 mg/L (+)-nootkatone [99]. As an application, most synthetic biology research on monoterreponoids and sesquiterpenes has focused on the high level of production in few compounds. However, a number of other monoterreponoids and sesquiterpenes have been produced in _E. coli_ or yeast, and other microbial systems by assembling and optimizing biosynthetic pathways that contain a heterologous MVA or MEP pathway, as well as GPP and FPP. Moreover, the field of synthetic biology in plants is still in its infancy. Synthetic biology research on plants needs reliable and effective techniques for compiling and transforming multi-component DNA constructions, such as a promoter and terminator. Reporter gene fusion is also a regular task in this field. Hence, optimizing this procedure is likely to result in significant productivity improvements. Traditionally, the required DNA construct has been designed using the restriction of endonuclease-mediated cleavage together with T4 DNA ligase-mediated joining. However, this approach takes a long time, and reliability along the sequence is not good for a large number of structures in a very efficient assembly [100; 101; 102]. Synthetic biology, which was inspired by engineering and mechanical assembly lines, uses standardized components to construct genetic creations. By using a Type IIS cloning system such as Golden Gate, MoClo, GoldenBraid, Loop Assembly, Fragment exchange, and others strategies for assembling synthetic constructs, high-throughput combinatorial libraries of synthetic constructs were easily constructed [103; 104]. Internal occurrences of the recognition sequence are a constraint of Golden Gate Cloning. Type IIS restricted enzymes are employed in Golden Gate Cloning. Such enzymes only cut at a single site beyond their recognition-binding site sequence. Basal detects the sequence 5\({}^{\prime}\)-GGTCTC-3\({}^{\prime}\). Each fragment that will be integrated into the target vector is bounded by Basal sites in the usual cloning process. [105]. Many of the reports included in the parts kit are also applicable to non-plant species. Such parts apply directly to multiple systems. Combinatorial pathway reconstruction includes all of the vector backbones and sequences needed for domesticating additional sequences and assembling them into single and multigene binary constructs [106]. These types of constructs are widely utilized in synthetic biology, and are a vital part of combinatorial bioengineering in plants.