By: Anurag Jakkula
Agriculture is the basis for civilization. There is no way around this hard fact. Throughout history, it has been proven that food is a human necessity, and its availability is the key to human advancement. Yet today, around 795 million people, or 1 in 9 people, do not have enough food on their plates. Furthermore, by burning fossil fuels and releasing greenhouse gases into the atmosphere, we put ourselves in the terrible predicament of global warming. According to the Third National Conference on Global Warming and Food Security, the next global food crisis will take place within the next four years. Our crops need to be more resistant, reliable, and efficient in order to cope with our fast changing environment. This can be achieved through the latest break-through in gene editing, CRISPR-Cas9.
CRISPR stands for “clustered regularly interspaced palindromic repeats.” Admiringly simple and incredibly effective, CRISPR-Cas9 is a gene-editing tool which has opened the door to numerous gene-editing related opportunities, such as gene defect corrections, disease protection, and of course, the improvement of crops. Adapted from the natural defense mechanism of archaea (single-celled organisms), CRISPR-Cas9 is the utilization of the CRISPR genetic sequence and Cas9 protein. A CRISPR sequence consists of recurring nucleotide sequences. In essence, a nucleotide is the simplest unit of “information” in DNA. In between these recurring sequences, a multitude of varying nucleotide sequences, called spacers, are present. Cas9 is the protein which performs the function of cutting DNA in a cell.
The CRISPR-Cas9 biological process was first observed in the virus defense mechanism of bacteria. When a bacterial cell survives a virus attack, a spacer from the virus’s DNA is inserted into the bacteria’s CRISPR DNA sequence. When the same type of virus attacks the bacteria again, an RNA polymerase immediately transcribes the relevant spacer of the CRISPR sequence into CRISPR RNA. This crRNA is complementary to the virus’s DNA, and therefore, Cas9 can use this crRNA along with tracrRNA as a “guide” to the target foreign DNA injected by the virus. Cas9 then makes its magnificent “double-stranded break,” cutting through both DNA strands and removing the problematic foreign DNA.
This biological defense mechanism has been adapted for gene-editing. In the paragraph above, it was mentioned that Cas9 uses crRNA as a guide. Genetic engineers can design and insert their own RNA to guide Cas9, called guide RNA. Cas9 then makes a cut at the targeted gene. The real gene-editing magic occurs within the cell’s healing process. In order to heal the cut, the gap is often filled in with a specific nucleotide sequence. Normally, a separate DNA region is used as the template for this filler. Genetic engineers leverage this healing process and provide the cell with their own DNA template. The resulting filler can include the nucleotide sequence of the engineer’s choice, and a gene can now be successfully “edited.” Seems genius? Well then, it’s no surprise that this year’s Nobel Prize in chemistry was given to Emmanuelle Charpentier and Jennifer Doudna of UC Berkeley for the development and documentation of this technology!
CRISPR-Cas9’s scope in the agriculture sector is almost limitless. Ground cherry tomatoes are considered a sweet delicacy by many. In addition, ground cherries prove to be nutritious with one cup of these cherries having 3 grams of protein, 16 grams of carbohydrates, and 1 gram of fat. These cherries are also rich in Vitamins A, C, and B-3, and are also a good source of Vitamin B-1, Vitamin B-2, iron, calcium, and phosphorus. However, these plants have a tendency to grow unpredictably and rapidly, making domestication difficult. Lemmon et al. has researched into the CRISPR gene-editing of this plant. By removing a portion of the groundcherry genome, the resulting variant grows in a more compact manner. When this modified variant enters the market, ground cherries will certainly have a more abundant appearance in supermarkets!
Another problem that CRISPR-Cas9 can fix is that those with Celiac Disease are not able to consume wheat due to their immunoreactivity with its gluten content. Sánchez-Léon et al. has researched into the manipulation of the a-gliadin gene in order to minimize this gluten content. When consumed by a Celiac patient, the modified wheat would result in 85% less immunoreactivity than non-modified wheat. The research has been completed, and the modified variant is currently undergoing its trial stage.