An Outlook on Global Regulatory Landscape for Genome-Edited Crops

Abstract

The revolutionary technology of CRISPR/Cas systems and their extraordinary potential to address fundamental questions in every field of biological sciences has led to their developers being awarded the 2020 Nobel Prize for Chemistry. In agriculture, CRISPR/Cas systems have accelerated the development of new crop varieties with improved traits-without the need for transgenes. However, the future of this technology depends on a clear and truly global regulatory framework being developed for these crops. Some CRISPR-edited crops are already on the market, and yet countries and regions are still divided over their legal status. CRISPR editing does not require transgenes, making CRISPR crops more socially acceptable than genetically modified crops, but there is vigorous debate over how to regulate these crops and what precautionary measures are required before they appear on the market. This article reviews intended outcomes and risks arising from the site-directed nuclease CRISPR systems used to improve agricultural crop plant genomes. It examines how various CRISPR system components, and potential concerns associated with CRISPR/Cas, may trigger regulatory oversight of CRISPR-edited crops. The article highlights differences and similarities between GMOs and CRISPR-edited crops, and discusses social and ethical concerns. It outlines the regulatory framework for GMO crops, which many countries also apply to CRISPR-edited crops, and the global regulatory landscape for CRISPR-edited crops. The article concludes with future prospects for CRISPR-edited crops and their products.

Keywords: CRISPR crops; CRISPR/Cas 3; genome editing 2; global regulations 4.

Figure 1

Schematic diagram of CRISPR/Cas9 mechanism. The system consists of Cas9 enzyme and gRNA, which bind with targeted double-stranded DNA to induce DSBs with blunt ends. The break can be repaired by either NHEJ or HDR. HDR requires a template, but NHEJ does not. Both mechanisms result in gene disruptions, deletions, and DNA editing containing the Cas9 gene and gRNA to the host genome at a random location.

Figure 2

Schematic diagram of CRISPR/Cas9. This system utilizes Cas9 enzyme and two RNAs: crRNA and tracrRNA. On binding with target DNA at the PAM site, it creates DSBs with blunt ends.

Figure 3

Schematic diagram of CRISPR/Cas12a and 12b. Both bind with target DNA upstream of PAM to induce DSBs with staggered ends. Cas12a utilizes crRNA. Cas12b utilizes crRNA and tracrRNA.

Figure 4

Schematic diagram of CRISPR/CasX. CasX is a dual-guided RNA enzyme utilizing crRNA and tracrRNA. It binds and cleaves dsDNA adjacent to an appropriate PAM site.

Figure 5

Schematic diagram of CRISPR/Cas14. This system utilizes Cas14 enzyme with two RNAs: crRNA and tracrRNA. It binds only ssDNA, and cuts without requiring a PAM site for recognition.

Figure 6

Schematic diagram of base editing with nickase Cas9 (nCas9). (a) ABE system uses nCas9 and adenine deaminase to catalyze transformation of adenine into guanine. ABE deaminates adenine to inosine (I), thus converting T-A to T-I. Repair machinery recognizes I as G and repair T-I as C-G; (b) CBE system utilizes nCas9 and cytidine deaminase to catalyze transformation of cytosine to uridine. Uracil glycosylase inhibitor (UGI) prevents U:G mismatch from being repaired back to C:G, and U is ultimately transformed into T.

Figure 7

Schematic diagram of prime editing, which involves fusing nCas9 with reverse transcriptase and a prime editing guide RNA (pegRNA). Prime editing systems edit DNA without causing DSBs, and the reverse transcriptase can accomplish various transitions, insertions, and deletions.

Figure 8

Schematic diagram of SDN1, SDN2, and SDN3. Nucleases such as ZFNs, TALENs, and CRISPR/Cas9 bind with target DNA to cause DSBs that are repaired by two different mechanisms. SDN1 does not need a template and results in gene disruptions through indels (small insertions or deletions of bases). SDN2 utilizes a homologous template and results in gene correction or modification at one or more positions. SDN3 requires a full gene as a template, and leads to gene replacement or foreign DNA insertion.

Figure 9

Schematic diagram showing how gene drives linked with CRISPR/Cas systems lead to forced inheritance, spreading the relevant trait throughout the whole population: (a) normal Mendelian inheritance; (b) gene drive-based inheritance.