Rafiq Islam (Kansas City): Thanks to gene editing technology, producers may soon be able to grow crops that are drought and flood tolerant, higher yield per acre, easier to harvest and transport, and more tastier, more nutritious, and less allergenic. Recently available on the market opal apple, takumi cauliflower or pearl grapes, high oleic soybean are just a few possibilities that will become reality in the very near future. Gene editing technology takes agriculture biotechnology beyond transgenic technology. The latter technology transfer gene “as is” from one species to another. Gene editing, on the other hand, essentially refine the endogenous responsible gene. This difference may justify the view that gene edited plants are not, like transgenic plants, genetically modified organisms (GMOs).
Both of these processes occur naturally or in breeding, but to obtain crops with desired phenotype (such as better size, color, or shape) takes time. Humans have been trying to improve crops for over 12000 years in a process known as agriculture. What’s different now is the range of possibilities arising from new genetic techniques. Still to bring a crop with expected phenotype to market normally takes 10 years with a cost of nearly $100 million and is only possible by a handful of big players in biotechnology industries. With the recent gene editing technology, the process become faster and cheaper, allowing many smaller players including academic labs to participate. The outcome of course is that consumers can expect many varieties with many different phenotypes of a single crop, fruit or vegetable.
The genome editor CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) has transformed many areas of biological sciences, as it is inexpensive and readily available. It can be used on crops that have smaller markets, rather than globally traded crops. In CRISPR, a guide made of RNA (known as gRNA) shuttles enzymatic scissors called Cas9 to exact place in a genome where edition to be made. Because plant cells have an extra-rigid cell wall compared with animal cells, it’s more difficult to deliver gRNA/Cas9 system into plant cells. So they are delivered by introducing into Agrobacterium that can breach the plant cell wall or put them on gold particles and shoot using what’s known as a gene gun. After selection, the edited cells are allowed to proliferate and develop to shoot, root and finally a plant, which may take six to nine months. Each stepdelivery, editing, and regeneration-is inefficient. Besides, inherent limitations of CRISPR technology such as off-target changes- incorrect changes made at target site or additional change introduced at different site, regeneration from cells is a massive bottleneck. This step must be optimized as some varieties may regenerate well, others, especially the elite (whose trait is desired) varieties are not. Thus any method that bypass the tissue culture method will be a big boon.
Both in academia and industry, scientists are thinking of new ways to deliver gene-editing reagents and to efficiently recover gene-edited plants. Recently in some plants, simply by pruning and adding editing reagents along with developmental regulators such as hormones to pruned sites allowed shoot formation. In others, use of DNA and RNA viral vectors to infect germline cells was successful. Since plants have mechanisms to eliminate viruses, there is typically no residual infection in the seeds of regenerated plants from viral vector.
Now, a major agricultural company has creatively developed a new method of using pollen from one genetically modified plant to carry CRISPR components into another plant’s cells. The method, published in Nature Biotechnology termed as HI-Edit, exploits an odd phenomenon known as haploid induction (HI) and promises to speed the creation of better and more versatile crops. The method allows pollen to fertilize plants without permanently transferring “male” genetic material to offspring, and the newly created plants only have a female set of chromosomes—making them haploid instead of the traditional diploid. The researchers took advantage of a corn line with a crippled gene that allows making its pollen able to trigger haploid induction transformed with gRNA and Cas9. The pollen of these transformed plants could then spread the gene editing machinery to other corn varieties. They also developed similar system for Arabidopsis, a genus of plants related to cabbage, broccoli, kale, and cauliflower. The method is a brilliant combining two technologies: haploid induction and genome editing and has huge promise developing new plants with desired gene editing.