Unlocking the Potential of CRISPR for Crops

As noted in last month’s Food, Medicine & Health column, CRISPR/Cas9 and CRISPR/Cpf1 technology has generated considerable interest in transforming plant cells (Yin, Gao, and Qiu 2017). In recent research initiatives, genes from the monocots corn, sorghum, sugarcane, and indica rice were successfully transformed, which suggests that these food crop transformations could contribute to advance plant growth and maturation (e.g., ripening); alter complex agronomic traits; increase nutritional value; expand plant varieties and crop yield; improve drought stress tolerance; and increase disease, pest, and herbicide resistance (Lowe, Wu, Wang et al. 2016).

More than 480,000 metric tons of rice (Oryza sativa) are produced annually, mostly from China and India; rice represents a significant crop (~18 billion pounds) for the United States as well. Regardless of the growing conditions, paddy rice or irrigated rice, there is a great need for reducing energy requirements in growing and harvesting this valuable crop. It is now increasingly clear that the gene-editing tool may successfully transform cultivars to require less water, increase nitrogen fixation, accelerate maturation, improve plant size, reduce fertilizer usage, decrease application of pesticides/herbicides, and elevate nutritional quality beyond that of their ancestors (Niiler 2018).

Critical applications of CRISPR to edit two groups of PYL genes that control an array of phytohormones, including abscisic acid, led several investigators at Purdue University and the Chinese Academy of Sciences to produce a rice cultivar with yield increased by 25%–31% (Miao, Xiao, Hua et al. 2018). Recognizing multiple genetic redundancies that impact plant growth, productivity, and stress tolerance, as well as seed dormancy, selected gene editing improved these characteristics to provide a balance associated with plant growth and stress adaptation appropriate for rice in paddy fields. In addition, new generation sequencing and genome-wide association studies have been applied to valuable agricultural crops, including rice. These tools contributed to modification of amylose content, seed length, and pericarp color of rice, and perhaps more importantly, an increased understanding of phenotypic variations that could contribute to improved agricultural practices (Wang, Xu, Vieira, et al. 2016) (Brachi, Morris, and Borevitz 2011).

Corn, wheat, soy, rice, barley, and sorghum are among the largest grain crops for livestock and humans in the United States, contributing approximately $150 billion to the U.S. economy. An increased understanding of the very complex wheat sequence databases and some of the polymorphisms for genes in different varieties may enhance plant characteristics through the identification of specific guide RNA (sgRNA) and subsequent developments of specific mutants, such as expanded dry farming of wheat (90% of wheat in the United States is dry farmed versus farmed using irrigation) and perhaps improve the sustainability of this valuable crop (Shan, Wang, Li, and Gao 2014) (Charmet 2011). Recent studies leveraging new generation sequencing emphasize the importance of under-standing the complex genome of wheat and will also contribute to more specific wheat breeding, thereby expanding desirable inheritable characteristics and important genetic targets for wheat improvement (Jia, Guan, Zhai, et al. 2018).

One approach to deliver CRISPR/Cas 9 to a crop such as corn (maize) is through a vector using E. coli and Agrobacterium. Preliminary data suggest these two CRISPR/Cas 9 modules may direct transgenic events with approximately 70% efficiency, thereby suggesting this approach represents a cost-effective tool to target mutagenesis for more desired agricultural characteristics (Char, Neelakandan, Nahampun, et al. 2017).

Application of RNA-guided Cas9 to barley generated mutations in 23% and 10% of targeted genes. Using an Agrobacterium-mediated transformation in the “Golden Promise” cultivar generated several transgenic lines. These stable mutations expanded the characterization of specific gene functions within barley despite evidence of non-target gene sequences (Lawrenson, Shorinola, Stacey et al. 2015).

CRISPR-based technologies represent an innovative approach that may improve the quality and quantity of the food supply. The application of these technologies in crops such as rice, corn, and tomatoes will impact and challenge those in food science, agriculture, ecology, and animal husbandry. CRISPR technologies could expand our understanding of plant immunity and plant production of an array of bioactives (phenolics, carotenoids, vitamin E, dietary fiber, and beta-glucan) thereby decreasing the use of many common agricultural adjuvants while enhancing crop qualities (Selle and Barrangou 2015).

Roger Clemens, DrPH, CFS, Contributing Editor
Adjunct Professor, Univ. of Southern California’s School of Pharmacy, Los Angeles, Calif.
[email protected]

Peter Pressman, MD, is director, The Daedalus Foundation ([email protected]).