# Biochemistry of Terpenes and Recent Advances in Plant Protection
## 2 Biosynthesis of Terpenes
### Elicitor-Induced Terpenes Biosynthesis  
Elicitors are molecules that trigger responses in plants. They are chemically diverse and act in a broad-spectrum manner [57]. Their renaissance has heightened the study of plant immunity. They are a possible remedy for biopesticides when recruited as external stimuli to induce transient accumulation of defense molecules in plants. Both biotic and  
Figure 4: Biosynthesis of various classes of terpen from IPP and DMAPP (structures were drawn and analyzed with ChemDraw software, version 20.0.0.41, and uploaded on BioRender.com to create the illustration).  
abiotic elicitors induce terpene biosynthesis. Biotic elicitors are molecules derived from living organisms such as fungi, bacterial, and cell wall fragments of plants. Abiotic elicitors are physical and chemical-related stresses with derivatives such as organic or inorganic compounds, salt, and heat stresses [58; 59]. While plants produce enough terpenes for their protection, inducing up-regulated production will meet commercial quantities for biopesticide development [58; 60].  
The advent of sophisticated whole-genome sequencing tools, such as Next-generation Sequencing (NGS) technologies, has demystified the identification of induced gene studies [61]. According to [PERSON] et al., several genes play a role in terpenes biosynthesis [62], and elicitor molecules can induce the high expression of the genes [63]. Elicitors can activate the methylerythntol phosphate (MEP) pathway to synthesize terpenes. Gene expression analysis of rice-cell suspension-culture treated with chitin induced early expression of MEP pathway genes for phytoalexins biosynthesis. In a related report, an HR-inducing elicitor protein, Mohrip1, isolated from _Magnaporthe oryzae_, was implicated by RNAseq and qPCR to induce high expression of oryzaein genes that eventually compromised _M. oryzae_ virulence [63]. [PERSON] et al. also demonstrated that salicylic acid could enhance diterpenes biosynthesis in _Sarcophtyton elrenberggi_[64]. In the last couple of years, transient expression of _N. benthamiana_ to reconstitute a partial or complete pathway for the synthesis of natural products has been reported [65; 66; 67]. This genetic modification has a significant effect on terpene production in higher titers. For example, momilactone diterpenoids induce allelopathy in rice plants. The momilactone gene transiently expressed in _N. benthamiana_ successfully exhibited allelopathic activities. Re-routing the diterpene biosynthesis site from the chloroplast to the cytosol was the technique. The reconstituted momilactone biosynthetic pathway synthesized momilactone by over 10-fold. Purified momilactone B from the _N. benthamiana_ stified _Arabidopsis thaliana_ germination [68]. [PERSON] and team also revealed that an endophytic fungal elicitor obtained from _Fusarium_ sp. E5 induced the accumulation of isoeuphpkeinensin and euphol in _Euphorbia pekinensis_ suspension cultures by 5.81% and 3.56%, respectively [69].  
A couple of research reports have also indicated that _Taxus cuspidate_ accumulates following methyl jasmonate (MeJA), hydrogen peroxide, salicylic acid (SA), and fungal elicitor (F3) treatment. These elicitors simultaneously enhanced the activity of 10-deacetylbaccatin III-10-O-acetyltransferase (10-DBAT) and cytochrome P450 monooxygenase concentration for high taxol synthesis [70; 71]. These shreds of evidenceindicate that elicitors are vital players in terpene synthesis that could meet commercial quantities.