The rapidly increasing global population, pest outbreaks, diseases, and abiotic stresses due to drastic changes in environmental conditions are a threat to agriculture and food production. Advanced breeding techniques are essential to increase crop productivity and nutritional value to cater to the demand for food across the globe. The CRISPR/Cas9 system offers the scope of plant breeding through modification of plant DNA using site-directed nucleases. The genetic modifications include gene silencing, gene knock-out, insertions, and gene editing using CRISPR/Cas9. This technique offers biotechnologists the scope to develop a sustainable and bountiful agricultural system by improving crop yield, quality, and increasing crop resistance to pests, diseases, droughts, and abiotic stresses.
Compared to conventional breeding techniques, CRISPR/Cas9 is a rapid technique that allows the modification of plant phenotypes within a short span of time. This technique can be used to modify any genetic sequence. However, the only limitation of the CRISPR technique is the availability of the appropriate PAM sequence. CRISPR technology also helps in the development of non-transgenic mutations in crops to help plants adapt to climatic variations and increase food supply.
CRISPR-based genome editing in plants such as tomatoes has helped in controlling fruit shape and size, flower proliferation, flowering time, and growth characteristics. Similarly, the mutation of GW2, GW5, TGW6 genes in rice helps in increasing rice seed size. Gene knockout of TaGW2 homeologs (a gene that negatively regulates seed size) in wheat using CRISPR also increases the seed width and length. Low-gluten wheat has also been genetically developed using the CRISPR/Cas9 system. Genetic editing in Brassica napus can help to produce more seeds with increased weight per silique. Thus, the CRISPR/Cas system can help in improving crop yield.
Tropical climates are more prone to pests, diseases, and abiotic stresses. Pests and diseases in crops can be a threat to food security and are estimated to cause 15% pre-harvest yield losses. Disruption or deletion of genes that increase susceptibility to diseases or stacking of genes that confer resistance to them can help in improving crop resistivity towards diseases. For e.g., rice crop is often infected with Blast disease, caused by the fungus Magnaporthe oryzae. CRISPR/Cas9 technology is capable of disrupting OsERF922 gene in rice that negatively regulates resistance to Blast disease. This disease infects other plants such as wheat, oats, and millets, and can be similarly eliminated.
Other genetically edited plants include papaya which is naturally susceptible to Papaya ringspot virus (PRSV). The transgenic varieties of papaya, i.e., “SunUp” and “Rainbow” are resistant to PRSV. Banana has also been genetically modified by editing MaSWEET genes to increase abiotic stress resistance, while targeting the MeMAPKKK gene in Cassava and GhRDL1 in cotton confers them drought resistance.