*3.2.3 Herbicide resistance improving*

Herbicides are the class of chemical compounds most widely used in agricultural practice. This is due to the fact that weeds cause significant damage to agriculture, reducing yields from competition with crops for resources [47]. However, despite the success of the herbicide using, their main disadvantage is their non-selective effect. To overcome this disadvantage, herbicide-resistant biotechnological varieties were created using genetic engineering methods. Currently all herbicide-resistant varieties approved for use have been obtained by transgenesis [11]. At the same time, GE methods are an effective tool for creating herbicide-resistant crop lines [7–10].

The main genes targeted by the GE in creating herbicide-resistant lines are the *EPSPS* and *ALS* genes. *ALS* gene encodes acetolactate synthase, participated in the biosynthesis of branched-chain amino acids, and the EPSPS gene encodes 5-enolpyruvylshikimate-3-phosphate synthase involved in the biosynthesis of essential plant aromatic amino acids [47]. Thus, based on the genes functions, it can be assumed that targeting *ALS* gene allows to obtain crop lines resistant to sulfonylurea herbicides, and *EPSPS* gene – to glyphosates [44]. Such lines were obtained by ODM-mediated targeted mutagenesis of the *ALS* gene in tobacco, rice, corn, and wheat [46]. Similar results of obtaining tobacco lines resistant to sulfonylurea were obtained by ZFN [18]. Also, other programmable nucleases (TALEN and CRISPR/ Cas9) were used to obtain herbicide-resistant lines of potato, rice, maize, and soybeans [44]. In addition, to obtain herbicide-resistant lines of rice (*Oryza sativa*), wheat (*Triticum aestivum*), potato (*Solanum tuberosum*), and watermelon (*Citrullus lanatus*), single base mutations were introduced into the ALS gene by CBE and ABE [39].

Along with this, CRISPR/Cas9-mediated point replacement of two nucleotides in the *EPSPS* gene allows to obtain glyphosate-resistant flax (*Linum usitatissimum*) and rice lines [44]. The targeting of the protoporphyrinogen oxidase (*PPO*) gene in *Arabidopsis* and exon 2 of inositol-1,3,4,5,6-pentakisphosphate-2-kinase (*IPK1*) gene in maize by ZFN was also used to obtain herbicide-resistant lines [18].
