### Tocopherol Synthesis
#### 2.1.3 Genetic Approaches for Boosting Isoprenoid Production in Plants
The levels of lipid peroxidation in the leaves of transgenic plants were also reduced under high light conditions compared to wild-type plants [128]. Mulberry plants overexpressing \(\upbeta\)-_OHase_ under the 35S promoter displayed increased resistance to UV radiation, high light (1000 \(\upmu\)mol photons/m\({}^{2}\) s), and heat stress (40 \({}^{\circ}\)C), compared to wild-type plants, resulting in reduced accumulation of ROS in the leaves [129]. In Lisianthus plants, overexpression of the Arabidopsis gene encoding \(\upbeta\)-OHase also led to a significant increase in carotenoid content (1.5-3 times) and, notably, enhanced accumulation of zeaxanthin (1.5-2 times) [130]. These transgenic plants were also more resistant to light stress [130]. Another way to increase zeaxanthin content in plants is by gene silencing of _zeaxanthin epicidase_ (see the carotenoid biosynthesis pathway in Figure 2). For example, using this approach on potato plants resulted in the growth of zeaxanthin content in tubers up to 130 times greater compared to the control plants [131]. LCYs are the key enzymes in the carotenoid biosynthesis pathway in higher plants (Table 1, Figure 2). Therefore, in many experimental studies on various plant species, LCY encoding genes are the targets for genome editing in order to increase the accumulation of bioactive lycopene. Tomato plants with a five-fold increase in lycopene content in fruits compared to unedited plants were transformed using the multiplex editing system CRISPR/Cas9. This approach resulted in simultaneous knockout of five genes: _Stay-green 1_ (_SGR1_) gene for the stimulation of lycopene synthesis, \(\varepsilon LCY\), and three \(\beta LCY\) genes, preventing cyclization of lycopene. Single, double, triple, and quadruple mutants of these genes were characterized, with the highest accumulation of lycopene in fruits for _SGR1_ single mutants [132]. Reducing the activity of \(\varepsilon LCY\) should lead to an increase in \(\upbeta\)-carotene and zeaxanthin, but it may also result in a decrease in lutein levels that could have negative consequences for plants. There are mentions in the literature about the specific reduction of \(\varepsilon LCY\) activity in tubers from potato plants obtained using antisense sequences of the \(\varepsilon LCY\) gene fragments introduced under the control of patatin promoter, which is specific for tuber tissues. In the resulting transgenic plants, carotenoid content in the tubers increased 2.5 times, and \(\upbeta\)-carotene content increased 14-fold [133]. In order to increase the provitamin A content, the fifth exon of the \(\varepsilon LCY\) gene was transformed in an embryogenic cell suspension of commercial banana varieties, specifically the Cavendish, Grand Naine,and Rasthali cultivars, followed by regeneration of transformed plants. The \(\beta\)-carotene content in the flesh of mature fruits of edited banana lines was six times higher compared to unedited fruits, while the amounts of lutein and \(\alpha\)-carotene were reduced [134]. Using CRISPR/Cas9 genomic technology, a single His in position 523 was replaced by Leu in \(\epsilon\)LCY in rice callus culture [135]. For precise targeted mutagenesis, a matrix delivery system based on a geminiviral replicon was used, which made it possible to significantly increase the frequency of homologous recombination and to obtain the transformed rice calli with a bright orange color with a success rate of 1.32%. The total content of carotenoids in the resulting edited callus lines was 6.8-9.6 times higher than in the wild-type callus. The authors also showed a decrease in the accumulation of ROS in the edited lines under salt stress conditions. Unlike traditional methods that rely on randomly selecting mutations and monitoring their effects, this work specifically targeted the \(\epsilon\)LCY gene for precise editing. It was performed as a follow-up to the study by [PERSON] et al.