### Tocopherol Synthesis
#### 2.1.3 Genetic Approaches for Boosting Isoprenoid Production in Plants
Another study involving _VTE1_-overexpressing Arabidopsis plants demonstrated a significant accumulation of plastochromanol in leaves, approximately 60 times higher than in wild-type plants [111]. Tobacco plants overexpressing the _VTE1_ gene from Arabidopsis exhibited increased resistance to drought stress, with reduced lipid peroxidation and H\({}_{2}\)O\({}_{2}\) content under stress conditions [112]. Rice plants overexpressing _VTE1_ (using a construct with two 35S promoters) demonstrated enhanced resistance to salinity stress, along with decreased H\({}_{2}\)O\({}_{2}\) levels under stress conditions [113]. It is known that \(\upalpha\)-tocopherol exhibits the highest biological activity. That is why many studies focus on the strategy of increasing the content of this form of tocopherol in plants. The enzyme VTE4 is involved in the final stage of \(\upalpha\)-tocopherol biosynthesis (Table 1, Figure 2). It has been used extensively for genetic engineering modifications of various plant species, including the increase of \(\upalpha\)-tocopherol content in soybean seeds to enhance their nutritional value. The expression of the gene encoding VTE4 from _Perilla fuftscens_under a seed-specific promoter (vicilin) resulted in a ten-fold increase in \(\alpha\)-tocopherol content in soybean seeds [114]. Overexpression of _AtVTE4_ in soybean seeds showed a four-fold increase in \(\alpha\)-tocopherol content [115], although the overall tocopherol content changed only slightly. In the study by [PERSON] et al. [116], screening was conducted to assess the impact of overexpression various tocopherol biosynthesis genes, both separately and in certain combinations (_VTE2 + VTE4_ and _VTE3 + VTE4_), ontocopherol content. The highest accumulation of tocopherols in the form of \(\alpha\)-tocopherol occurred in Arabidopsis plants with simultaneous overexpression of _VTE2_ and _VTE4_, approximately six times higher than in the wild-type plants. Additionally, a high level of tocopherol accumulation was demonstrated in transgenic Arabidopsis plants with increased VTE2 content [116]. Interestingly, transgenic _Codonopsis lancolata_ plants overexpressing the Arabidopsis gene _AtVTE4_ exhibited a higher antimicrobial activity against _Staphylococcus aureus_ and _E. coli_ compared to the wild-type plants [117]. The increased antimicrobial activity may be associated with the elevated accumulation of tocopherols in these transgenic plants that was approximately six times higher than in the leaves of wild-type plants. Because UQ is a component of the respiratory chain common to all eukaryotes, gene transfer from other eukaryotic organisms, such as yeast, into plant genomes is feasible. The expression of _CoQ2_ from yeast led to a six-fold increase in ubiquinone content in tobacco leaves [118]. The resulting transgenic plants showed increased resistance, compared to the wild-type plants, against salinity stress (300 mM NaCl) and oxidative stress induced by the addition of 50 uM methyl viologen [118]. Overexpression of the SPS enzymes (Figure 2) in different plant species has led to increased accumulation of UQ or PQ, depending on the specific variant of the _SPS_ gene used. In _Salvia uniformiha_ plants, the overexpression of the _SmPP1_ gene resulted in approximately a 2-fold increase in PQ content, while the overexpression of the _SmPP2_ gene led to a 1.5-fold increase in UQ content [119]. In Arabidopsis plants with the overexpression of _SPS1_, the content of PQ increased approximately 1.5- to 2-fold, and the content of plastochromanol increased approximately 3-fold compared to that in wild-type plants [48]. These transgenic plants showed greater resistance to high light conditions (1300 umd photons/m\({}^{2}\) s) compared to the wild-type plants: they exhibited decreased lipid peroxidation and PS II photoinhibition. Since there was a significant increase in plastochromanol content in these plants, it can be speculated that the increased resistance is determined by the higher plastochromanol content.