Gene targeting and editing in crop plants: a new era of precision opportunities

With increasing global food demands in the face of challenging biotic and abiotic pressures on crop production, there is a vital need for good crop improvement strategies. Gene editing and gene targeting using designer nucleases are relatively new, sophisticated approaches that can be used for crop improvement. Designer nucleases are molecules that can be engineered to cleave virtually any endogenous DNA target sequence, making this technology inherently more powerful over current, essentially random mutation strategies. These molecules can also be used to promote targeted DNA insertions and homologous recombination. Further modifications of these molecules can convert them into designer transcription factors that can activate or suppress a gene of choice. Four designer nuclease platforms are currently available: meganucleases, zinc finger nucleases, TALENs and the more recently developed CRISPR/Cas9 system. All four of these systems have been shown to function in crop plants and have been used for site-specific gene targeting and gene editing. Herein, we describe the basis of each designer nuclease platform, highlighting the advantages and disadvantages of each, and give examples of their application in crop improvement.