# Trepenes and Trepenoids in Plants: Interactions with Environment and Insects
## 3 Potential Agricultural Biotechnology Applications
With nanotechnology, encapsulated terpenoids can be used to trap insect pests. A study [87] evaluated and proposed a potential system to trap _Bemisiu tabaci_ through attraction by geraniol encapsulated in chitosan/gum Arabic nanoparticles. Other than promoting crop yield through weed control, pest management, and pollination, one of the direct impacts on agriculture by mustering terpenoid biosynthesis is to enhance or alter the scents and flavors of products. There are cases of increased production of monoterenes in transgenic plants such as tomato, carnation, potato, mint, and tobacco by overexpressing the corresponding _TPS_ genes or _CYP450_ genes or regulating TFs, promoters, etc. [107; 108; 109; 110]. The same goes for medicinal plants. A sesquiterpene (artemisinin) produced by _Artemisia annua_ is regarded as an effective therapy against malaria-causing _Plasmodium falciparum_ strains [111]. Artemisinin biosynthesis can be upregulated via two TFs (AaERF1 and AaERF2) belonging to the AP2/ERF family [112]. More engineering approaches such as suppressing the metabolic pathways that compete with the biosynthetic pathways of terpenoid or regulating endogenous phytohormones can be adopted to adjust terpenoid production [113] in response to the challenging agriculture environment. Abiotic stresses including drought, flooding, changes in salinity, heat, cold, and high irradiance have caused a decline in plant primary production and crop losses worldwide. Hence, mitigating the negative impacts of these factors is imperative to address pressing issues regarding food quality and security. Considering the important roles of terpenoids in the abiotic stress response, metabolic engineering towards a more stable and efficient production of volatile and essential terpenoids may provide a long-term solution. Metabolic engineering of plant terpenoids has been reviewed [114], and while increasing the production of terpenoids is the desired ultimate goal, it comes with a cost, particularly because of the possibility of perturbing cellular homeostasis. Thus, it is equally important to consider a different paradigm in this matter. A preferential increase in precursor flux in one pathway might inadvertently deplete other pathways with shared precursors needed for the production of equally essential metabolites, and unregulated production of volatile terpenes may lead to cytotoxicity. In retrospect, the key role of phytohormones in plant defense and stress responses is widely recognized. These hormones activate stress signaling in a global manner, culminating with an integrated stress response including, but not limited to, increased production of volatile terpenes [115]. A proportionate regulation of biochemical pathways in response to changing environmental conditions is intuitively less stressful and perturbing to plants that are already experiencing stress. Hence, modifying the production of stress-associated phytohormones and modulating their potentiating effect on the stress response may provide a more suitable alternative to increasing volatile terpene production, while keeping any adverse effect that might spontaneously arise at bay.