Plants are exposed to a variety of abiotic and biotic stresses leading to increased formation of reactive oxygen species (ROS) in plant cells. ROS are capable of oxidizing proteins, pigments, lipids, nucleic acids, and other cell molecules, disrupting their functional activity. During the process of evolution, numerous antioxidant systems were formed in plants, including antioxidant enzymes and low molecular weight non-enzymatic antioxidants. Antioxidant systems perform neutralization of ROS and therefore prevent oxidative damage of cell components. In the present review, we focus on the biosynthesis of non-enzymatic antioxidants in higher plants cells such as ascorbic acid (vitamin C), glutathione, flavonoids, isoprenoids, carotenoids, tocopherol (vitamin E), ubiquinone, and plastoquinone. Their functioning and their reactivity with respect to individual ROS will be described. This review is also devoted to the modern genetic engineering methods, which are widely used to change the quantitative and qualitative content of the non-enzymatic antioxidants in cultivated plants. These methods allow various plant lines with given properties to be obtained in a rather short time. The most successful approaches for plant transgenesis and plant genome editing for the enhancement of biosynthesis and the content of these antioxidants are discussed.

Plants are exposed to a variety of abiotic and biotic stresses leading to increased formation of reactive oxygen species (ROS) in plant cells. ROS are capable of oxidizing proteins, pigments, lipids, nucleic acids, and other cell molecules, disrupting their functional activity. During the process of evolution, numerous antioxidant systems were formed in plants, including antioxidant enzymes and low-molecular-weight non-enzymatic antioxidants. Antioxidant systems perform neutralization of ROS and therefore prevent oxidative damage of cell components. In the present review, we focus on the biosynthesis of non-enzymatic antioxidants in higher plant cells such as ascorbic acid (vitamin C), glutathione, flavonoids, isoprenoids, including carotenoids, tocopherol (vitamin E), ubiquinone and plastoquinone. Their functioning and their reactivity with respect to individual ROS are described. The review is also devoted to the modern genetic engineering methods, which are widely used to change the quantitative and qualitative content of the non-enzymatic antioxidants in cultivated plants. These methods allow to obtain various plant lines with given properties in a rather short time. The most successful approaches for plant transgenesis and plant genome editing for the enhancement of the biosynthesis and the content of these antioxidants are discussed.

Targeted DNA integration into known locations in the genome has potential advantages over the random insertional events typically achieved using conventional means of genetic modification. We investigated the possibility of obtaining a suspension cell culture of Arabidopsis thaliana carrying a site-specific integration of a target gene encoding modified human interferon (dIFN) using endonuclease Cas9. For the targeted insertion, we selected the region of the histone H3.3 gene (HTR5) with a high constitutive level of expression. Our results indicated that Cas9-induced DNA integration occurred with the highest frequency with the construction with donor DNA surrounded by homology arms and Cas9 endonuclease recognition sites. Among the monoclones of the four cell lines with knock-in studied, there is high heterogeneity in the level of expression and accumulation of the target protein. The accumulation of dIFN protein in cell lines with targeted insertions into the target region of the HTR5 gene does not statistically differ from the level of accumulation of dIFN protein in the group of lines with random integration of the transgene. However, one among the monoclonal lines with knock-in has a dIFN accumulation level above 2% of TSP, which is very high.

The review presents current data on molecular genetic mechanisms of suppression of the gene (transgene) expression in plants at the transcriptional level. The stages of RNA-directed DNA methylation are discussed in detail. Mutations affecting transcriptional gene inactivation without altering nucleotide sequence methylation are described.

Targeted DNA integration into known locations in the genome has potential advantages over the random insertional events typically achieved using conventional means of genetic modification. We studied the presence and extent of DNA rearrangements at the junction of plant and transgenic DNA in five lines of Arabidopsis thaliana suspension cells carrying a site-specific integration of target genes. Two types of templates were used to obtain knock-ins, differing in the presence or absence of flanking DNA homologous to the target site in the genome. For the targeted insertion, we selected the region of the histone H3.3 gene with a very high constitutive level of expression. Our studies showed that all five obtained knock-in cell lines have rearrangements at the borders of the integrated sequence. Significant rearrangements, about 100 or more bp from the side of the right flank, were found in all five plant lines. Reorganizations from the left flank at more than 17 bp were found in three out of five lines. The fact that rearrangements were detected for both variants of the knock-in template (with and without flanks) indicates that the presence of flanks does not affect the occurrence of mutations.

The phenomenon of transgene silencing was first observed shortly after the generation of the initial transgenic plants. The vast body of experimental data accumulated since then constitutes an invaluable resource for dissecting the mechanisms of epigenetic gene regulation. Silencing operates at either the transcriptional (TGS) or post-transcriptional (PTGS) level and is predominantly mediated by small interfering RNAs (siRNAs). Although these two epigenetic pathways involve distinct sets of proteins and enzymes, they share fundamental mechanistic features: the generation of double-stranded RNA (dsRNA), its processing into siRNAs by DICER-LIKE (DCL) enzymes, and the assembly of an Argonaute-centered effector ribonucleoprotein complex (RISC). Guided by sequence-specific siRNAs, this complex identifies complementary target sequences with high precision. A comprehensive understanding of these regulatory pathways enables the targeted induction or suppression of specific plant genes. This review traces the history of experimental findings regarding the loss of recombinant gene activity in transformants and their progeny, which collectively established the foundation for elucidating the molecular mechanisms of transgene silencing.