## 3 Results
### The Screening of Transgenic Strain of C. reinhardtii  
The RPL23-SmMYB98-RPL23-ble plasmid was transformed into the cells of _C. reinhardtii_ using the electroporation method. After 14 days of recovery, we have observed visible green colonies of transformed cells of _C. reinhardtii_ and we then transferred them to fresh TAP media containing 100 \(\upmu\)g/mL ampicillin and 8 \(\upmu\)g/mL zeocin. We have obtained more than 200 colonies and a frequency of transformation (3 \(\times\) 10\({}^{-8}\)) was noticed. After that, in order to screen positive transformants, genomic PCR targeting the MYB36 gene was carried out. According to PCR results, no target bands were obtained in non-transgenic cells of _C. reinhardtii_ (Figure S1).  
MYB36 Transcriptional Factors UIrregulate the MEP Biosynthetic Pathway in Overexpression Lines of C. reinhardtii  
As MYB transcriptional factors have a critical role in the production of terpenoids in plants, we hypothesized that our candidate MYB36 gene stimulates the biosynthesis of terpenoid precursors in the cells of _C. reinhardtii_. The general building blocks of entire terpenoids are isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). In _C. reinhardtii_, these precursors are uniquely synthesized by the MEP pathway, while the MVA biosynthetic pathway is absent in _C. reinhardtii_[34]. So, transcript levels of key structural genes involved in the MEP pathway were assessed in MYB36-overexpression lines by qPCR analysis. The transcript level of gene encoding enzymes _CrDXS_, _CrDXR_, _CrGPS_, _CrGPS_, _CrPS_, _CrFPS_, _CrFPPS_, _CrIPP2_, _CrIPP1_, _CrIDS_, _CrCMS_, and _CrCMK_ were investigated by qPCR (Figure 3). The outcomes from this study indicated that the expression levels of the above-mentioned genes were higher than the wild type of _C. reinhardtii_ CC124. _DXS_ and _DXR_ play a key function in the regulation of flux in the MEP pathway of land plants [35]. Overexpression of _DXS_ accumulates in the isoprenoid production in transgenic Arabidopsis, suggesting that DXS catalyzes one of the rate-limiting steps involved in the biosynthetic pathway of MEP [36]. _DXR_ and _HDR_ are other enzymes that play a function as rate-limiting factors in the formation of IPP and DMAPP [37]. Recently, investigations on DXS have attained more attention in order to modify terpenoid metabolisms. Methyl jasmonate (MeJ)-treated _C. reinhardtii_ cells increase in the expression of _DXS_ leading to an increase in the triterpen squalene synthesis [38]. Heterologous overexpression of _Salvia pomifera DXS_ in _C. reinhardtii_ improved flux toward diterpenoid production via the MEP biosynthetic pathway [24]. MEP plays a crucial function in the regulation of the MEP biosynthetic pathway. The MEP is the initial obligated precursor of the pathway and triggers the MDS gene transcript level [39]. The change in metabolism regarding the IPP production implies a promising accumulation of geranyl pyrophosphate (GPP) and farnesyl pyrophosphate (FPP) in the MYB36-overexpression lines. The expression levels of FPP and GGPP were remarkably higher in the MYB36-overexpression C. _reinhardtii_ lines compared to parent lines. Our results were similar to the previous study, which indicated that the accumulation of GGPP expression in Mej-treated cells of C. _reinhardtii_ improved the terpenoid production [38]. The incidence of a metabolic change toward the production of triterpenoids, such as squalene, is also supported by the accumulation of FPP.