## 1 Introduction  
Over the last 25 years, nearly 65,000 chemical structures of terpenoids have been discovered, making terpenids the class of natural products with the greatest structural diversity [1; 2]. Terpenoids are involved in a variety of important functions in regulating plant growth (especially for terpenoid lactones) and play an ecological role in attracting pollinators [3]. Terpenoids are grouped into different classes based on the number of 5-carbon building blocks [4; 5; 6; 7]. All terpenoids are derived from the common phosphorylated five-carbon (C5) building units, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) [8]. There are two major pathways involved in the biosynthesis of terpenoids, namely, the mevalonate (MVA) pathway, which is primarily found in eukaryotes, and the methylerythrhitol phosphate (MEP) pathway (non-mevalonate pathway), which is primarily found in prokaryotes and plant chloroplasts [9; 10; 11]. For sesquiterpene biosynthesis, IPP and DMAPP undergo condensation to form famesyl pyrophosphate (FPP), which is catalysed by the enzyme FPP synthase. The resulting linear FPP undergoes electrophilic cyclisation and rearrangement to form acyclic and non-acyclic sesquiterpenes, based on the sesquiterpene synthase enzyme reactions [12; 13]. In particular, monoterpenes and sesquiterpenes are commonly present in plant essential oils, which are widely utilised for commercial purposes, such as fragrances, cosmetics, pharmaceuticals, medicine, biofuel precursors, and industrial materials [14; 15]. To date, over 7000 sesquiterpenes (C15) with different hydrocarbon skeletons and stereo-chemically structures have been reported [16]. Studies on naturally derived 15-carbon terpenids in aromatic herbal plants as anti-malarial, anti-microbi, and insecticidal agents have also increased over the last several years [17]. Hence, many sesquiterpenes are founds as major components of fruits and vegetables, floral scents, and essential oils of herbs. In previous studies, a number of genes encoding the sesquiterpene enzymes, which control the key steps of secondary metabolic pathways, have been extensively cloned and characterized from a number of herbal plant species. For example, squalene synthase from _Tripterygium wilfordii_[18], germacrene A synthase from _Adillae milfefolium_[19], dimenol synthase from _Valeriana officinalis_[20], E-E-farnesol synthase and \(\alpha\)-bisabolene synthase from _Gingko biloba_[21], \(\alpha\)-humulene synthase from _Zingiber zerumbet_ [PERSON] [22], (+)-epi-\(\alpha\)-bisabolol synthase from _Lippia dulcis_[23], \(\beta\)-caryophyllene synthase from _Octimum basilicum_ L. [24], \(\alpha\)-humulene synthase from _Zingiber zerumbate_ [PERSON] [25], and Germacrene D synthase from _Zingiber officiale_[26]. _Polygonum minus_ (syn. _Persicaria minor_) is a herbal plant that originated from Southeast Asia and belongs to the Polygonaceae family. In Malaysia, _P. minus_ is locally known as a 'kesum', and is commonly used as a food additive and flavouring agent. Many studies have been carried out because of the popularity of the _P. minus_ as a potential medicinal plant with high antioxidant and antimicrobial activities and strong anti-inflammatory properties [27; 28; 29; 30]. _P. minus_ is an economically important herbal plant because of its essential oils, which cause it to emit a strong scent from a simple mixture of terpenoid hydrocarbons (monoterpenoids and sesquiterpenoids), including \(\beta\)-farnesene, \(\alpha\)-farnesene, nerolidol, farnesol, caryophyllene, \(\alpha\)-bergamotene, and drimeenol [31; 32]. Other characteristic components that have been identified from _P. minus_ include aldehydes (decanal and dodecanal), esters, and organic acids [33]. Moreover, recent studies have revealed that the sesquiterpenes compounds are the main contributors to the characteristic fragrance of this plant [34]. These studies have shown the potential for developing _P. minus_ as a resource to produce natural products.