Genome-editing tools provide advanced biotechnological techniques that …. have been utilized in a wide variety of plant species to characterize gene functions and improve agricultural traits …. [W]e review novel breakthroughs that are extending the potential of genome-edited crops [and discuss] [fu]ture prospects for integrating this revolutionary technology with conventional and new-age crop breeding strategies.

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The risks involved in altering genomes through the use of genome-editing technology are significantly lower than those associated with GM crops because most edits alter only a few nucleotides, producing changes that are not unlike those found throughout naturally occurring populations.

Table 1: Crop traits that have been improved by genome-editing techniques

Crop species Gene editor Target gene DNA repair type Target trait Reference Maize ZFNs ZmIPK1 HR Herbicide tolerant and phytate reduced maize [14] Maize ZFNs ZmTLP HR Trait stacking [15] Rice ZFNs OsQQR HR Trait stacking [16] Rice TALENs OsSWEET14 NHEJ Bacterial blight resistance [18] Wheat TALENs TaMLO NHEJ Powdery mildew resistance [19] Maize TALENs ZmGL2 NHEJ Reduced epicuticular wax in leaves [20] Sugarcane TALENs COMT NHEJ Improved cell wall composition [21] Sugarcane TALENs COMT NHEJ Improved saccharification efficiency [22] Soybean TALENs FAD2-1A, FAD2-1B NHEJ High oleic acid contents [23] Soybean TALENs FAD2-1A, FAD2-1B, FAD3A NHEJ High oleic, low linoleic contents [24] Potato TALENs VInv NHEJ Minimizing reducing sugars [25] Rice TALENs OsBADH2 NHEJ Fragrant rice [26] Maize TALENs ZmMTL NHEJ Induction of haploid plants [27] Brassica oleracea TALENs FRIGIDA NHEJ Flowering earlier [28] Tomato TALENs ANT1 HR Purple tomatoes with high anthocyanin [29] Rice CRISPR/Cas9 LAZY1 NHEJ Tiller-spreading [39] Rice CRISPR/Cas9 Gn1a, GS3, DEP1 NHEJ Enhanced grain number, larger grain size and dense erect panicles [40] Wheat CRISPR/Cas9 GW2 NHEJ Increased grain weight and protein content [41] Camelina sativa CRISPR/Cas9 FAD2 NHEJ Decreased polyunsaturated fatty acids [42] Rice CRISPR/Cas9 SBEIIb NHEJ High amylose content [43] Maize CRISPR/Cas9 Wx1 NHEJ High amylopectin content [44] Potato CRISPR/Cas9 Wx1 NHEJ High amylopectin content [45] Wheat CRISPR/Cas9 EDR1 NHEJ Powdery mildew resistance [46] Rice CRISPR/Cas9 OsERF922 NHEJ Enhanced rice blast resistance [47] Rice CRISPR/Cas9 OsSWEET13 NHEJ Bacterial blight resistance [48] Tomato CRISPR/Cas9 SlMLO1 NHEJ Powdery mildew resistance [49] Tomato CRISPR/Cas9 SlJAZ2 NHEJ Bacterial speck resistance [50] Grapefruit CRISPR/Cas9 CsLOB1 promoter NHEJ Alleviated citrus canker [51] Orange CRISPR/Cas9 CsLOB1 promoter NHEJ Citrus canker resistance [52] Grapefruit CRISPR/Cas9 CsLOB1 NHEJ Citrus canker resistance [53] Cucumber CRISPR/Cas9 eIF4E NHEJ Virus resistance [54] Mushroom CRISPR/Cas9 PPO NHEJ Anti-browning phenotype [55] Tomato CRISPR/Cas9 SP5G NHEJ Earlier harvest time [56] Tomato CRISPR/Cas9 SlAGL6 NHEJ Parthenocarpy [57] Maize CRISPR/Cas9 TMS5 NHEJ Thermosensitive male-sterile [58] Rice CRISPR/Cas9 OsMATL NHEJ Induction of haploid plants [59] Tomato CRISPR/Cas9 SP, SP5G, CLV3, WUS, GGP1 NHEJ Tomato domestication [60] Rice CRISPR/Cas9 ALS HR Herbicide resistance [61] Rice CRISPR/Cas9 ALS HR Herbicide resistance [62] Rice CRISPR/Cas9 EPSPS NHEJ Herbicide resistance [63] Rice CRISPR/Cas9 ALS HR Herbicide resistance [64] Soybean CRISPR/Cas9 ALS HR Herbicide resistance [65] Maize CRISPR/Cas9 ALS HR Herbicide resistance [66] Potato CRISPR/Cas9 ALS HR Herbicide resistance [67] Flax CRISPR/Cas9 EPSPS HR Herbicide resistance [68] Cassava CRISPR/Cas9 EPSPS HR Herbicide resistance [69] Maize CRISPR/Cas9 ARGOS8 HR Drought stress tolerance [70]

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[T]he CRISPR/Cas -gene-editing] system is characterized by its simplicity, efficiency, and low cost, and by its ability to target multiple genes. Because of these characteristic features, CRISPR/Cas9 …. may be an effective solution to a variety of problems in plant breeding. To date, many crops such as rice, maize, wheat, soybean, barley, sorghum, potato, tomato, flax, rapeseed, Camelina, cotton, cucumber, lettuce, grapes, grapefruit, apple, oranges, and watermelon have been edited by this technique

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With the progress already made in the development of genome-editing tools and the development of new breakthroughs, genome editing promises to play a key role in speeding up crop breeding and in meeting the ever-increasing global demand for food. Moreover, the exigencies of climate change call for great flexibility and innovation in crop resilience and production systems. In addition, we must take into account government regulations and consumer acceptance around the use of these new breeding technologies.

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