When we talk about the use of CRISPR-Cas9 technology, it’s usually in the context of developing treatments for human diseases. But there’s another aspect to the technology that has potential to have just as much impact on our lives: its use in the genetic modification of food crops.
Gene editing is not new to agriculture, with a historic approach of selective breeding to more modern innovations in DNA editing. Today, CRISPR-Cas9 is being rapidly adopted as a gene editing tool for agricultural applications. The CRISPR-Cas9 system is unmatched in efficiency and ease-of-use since it requires a single target specific guide sequence coupled with a single nuclease.
We’re seeing that the prime candidates for Cas9-mediated editing are plants whose genotypes are well characterized and where genotype to phenotypic outcomes are better understood. In these crops, there is a constant drive to improve productivity and yield by addressing issues related to disease and growth, while enhancing favorable traits such as oils and starch.
Overcoming DNA-only limitations
Attending CRISPR AgBio Congress a few weeks ago, the excitement of adapting CRISPR-Cas9 technology to the agricultural industry was apparent. Researchers presented DNA-free CRISPR-Cas9 approaches to plant genome editing, where the Cas9 enzyme is directly introduced to the cells with the guide RNA (gRNA). This method allows scientists to overcome some issues common to a DNA-only approach.
In the DNA-only approach, integration of the Cas9 and gRNA DNA expression cassette can disrupt genes, increase off-target mutations, and may require a long process of back crossing to resolve, and use a selection marker. Many of these issues are resolved by using a DNA-free CRISPR-Cas9 gene editing method.
To date, both corn and wheat have been successfully edited with the DNA-free approach. A 2016 article in Nature Communications demonstrated how a ribonucleoprotein (RNP) composed of Cas9 protein + gRNA complex can be introduced to maize embryo cells via biolistic delivery with lower off-site mutation frequency than DNA delivery methods. Also, RNPs were recently delivered to bread wheat via biolistics with the result that no off-target mutations were detected by deep sequencing.
Other scientists have successfully propagated plant protoplasts and used DNA-free RNP delivery via biolistics or transfection. One recent paper demonstrated RNP delivery to Arabidopsis thaliana, tobacco, lettuce and rice protoplasts, and found gene editing frequencies comparable to DNA vector delivery.
Adapting the regulatory framework
Dealing with regulations is a common part of working in the biotechnology field, and the agriculture industry is no exception. During CRISPR AgBio Congress, there were many discussions about the regulatory environment and learning specifically how CRISPR-Cas9 gene editing fits (or doesn’t fit) current guidelines.
Presently, we are seeing some movement to help shape regulations that affect Cas9 technology as it pertains to agriculture. Both the Food and Drug Administration (FDA) and the U.S. Department of Agriculture (USDA) have recently requested input from the public and companies on various CRISPR-Cas9 topics such as:
- FDA: Foods Derived From Plants Produced Using Genome Editing
- USDA: 2017 Proposed Biotechnology Regulations
How the use of CRISPR-Cas9 and especially DNA-free techniques will be viewed by the public and regulatory agencies is still being determined. Use of RNPs is seen as a positive technique to enhance safety and increase productivity in the food supply.
What’s ahead for agricultural use of CRISPR-Cas9
There will always be great demand for technologies that help ensure access to a reliable food supply. One notable takeaway from the CRISPR AgBio Congress is the huge demand for consistent and reliable gene editing nuclease manufacturing. Agricultural technology companies require Cas9 and Cpf1 nucleases that feature scalable manufacturing protocols for high purity and consistent lot-to-lot activity. You can see the benefits to this consistency with Aldevron's Cas9 and Cpf1 nucleases.
It’s impressive how much the adoption of CRISPR-Cas9 technology has grown for agricultural research in the relatively short time it’s been available. Given the wide range of topics discussed during CRISPR AgBio Congress, the technology is going to greatly affect our day-to-day living, far beyond the medical applications that were originally envisioned.