Improvement of Crops Using the CRISPR/Cas System: New Target Genes

Abstract

Successful application of the CRISPR/Cas genome editing system to various crops largely depends on the correct choice of target genes that may be purposefully changed to improve yield, quality, and resistance to biotic and abiotic stressors. The objective of this work was systematizing and cataloguing the information on the confirmed target genes for crop improvement. The latest systematic review was presented on peer-reviewed scientific papers (indexed in the Scopus database) published before August 17, 2019. The present study covers the period from August 18, 2019 to March 15, 2022. The search according to the given algorithm revealed 2090 publications, and their analysis showed that only 685 original papers contained the results of gene editing for 28 crops (the search included 56 crops). A significant part of these publications described the application of genome editing to target genes previously identified in similar works or the studies were associated with reverse genetics, while only 136 publications contained data on editing new target genes whose modification was aimed at improving plant traits important for breeding. The total number of target genes in cultivated plants that were edited to improve properties of breeding value over the entire period of the CRISPR/Cas system application was 287. A detailed analysis of the editing of new target genes is presented in this review. The studies were most often aimed at increasing plant productivity and disease resistance as well as improving the properties of plant materials. Observations are made whether it was possible to obtain stable transformants at the time of publication and whether the editing technique was applied to non-model cultivars. For a number of crops, however, the range of modified cultivars was significantly expanded, specifically for wheat, rice, soybean, tomato, potato, rapeseed, grapevine, and maize. In a vast majority of cases, agrobacterium-mediated transformation was used to deliver the editing construct; less often it was bioballistics, protoplast transfection or haploinducers. The desired change in traits was most often achieved by gene knockout. In some cases, knockdown and nucleotide substitutions were applied. The base-editing and prime-editing approaches have increasingly been used to make nucleotide substitutions in crop genes. The emergence of a convenient CRISPR/Cas editing system helped to significantly intensify the development of molecular genetics specific to many crop species.