CRISPR, Gene Editing And Its Uses In Agriculture

CRISPR or Clustered Regularly Interspaced Short Palindromic Repeats (Broad Institute, 2019) is a relatively new discovery in genetic sciences with many useful applications across many fields. CRISPR is extracted from a bacterium and was initially thought of to be a part of bacterial immune system. It has what are known as spacer sequences that contain past genetic code of bacteriophages and destroys them when they return. (Broad Institute, 2019) First proof of this was on 23 March 2007 (Ishino, et al., 2018) By altering the DNA of the spacers of the CRISPR or the crDNA (CRISPR DNA) it is possible to alter the nucleotide sequence of a gene to be as you desire because the CRISPR can cut through the DNA site and mutate it to a desired nucleotide sequence. (Vidyasagr & Aparna, 2018) Evidently, altering DNA can have major impacts on lifeforms and make them express genes that they wouldn’t otherwise and this can be very beneficial in numerous different scenarios. An example of this is changing the DNA of a person to help permanently cure their genetic disorders or gene surgery. Editing cells to produce precursors to drugs for medication is another use. The final example I will mention and the example I will elaborate in is agriculture.

CRISPR Cas9 is used in multiple fields of agriculture be it in grains or vegetables I will highlight the advantages of three different uses of CRISPR in these fields and then talk about the disadvantages. Originally, in order to get the highest quality crop be it in size or taste, cross-breeding was the most efficient method (Fiaz, et al., 2019). Rice grain quality has been at the forefront of research as over 3.5billion people feed on it which is almost half the population of earth. (Fiaz, et al., 2019) The main aspect of rice grain quality are determined by the micronutrients and biologically active components within the grains (Lau, et al., 2015)Multiple quantitative trait loci have been identified within these rice grains to affect certain parts of the growth of the rice be it qBRR3 & qBRR5 which regulate grain width and length (Lou, et al., 2009), or the Waxy gene (Wx) which affects the amylose content of a rice grain (Lapitan, et al., 2009) and its has been shown that rice with low amylose content tends to be sticky where rice with high amylose content tends to cook firm and dry (International Rice Research Institute, 2006) which can be beneficial depending on how you want your rice to be used. The improvement of rice quality using CRISPR has proven to be cost effective and incredibly efficient. The first step of this process is to identify the gene/(s) you wish to edit, so for example I want a rice grain that is low in amylose. I would need to edit the Waxy gene. Obviously, there are multiple different genes that affect each of these characteristics. Amylose content is determined by a single dominant gene however thus mutating this gene to make it not work has been proven to lower the amylose content. Therefore, by using CRISPR Cas9 to identify this specific gene and thus altering it so that it is no longer expressed we can get our desired characteristic (Zhu, et al., 2018). CRISPR can be used for crops in ways other than improving the quality of the crop or the taste of the crop.

Plants can also suffer from diseases that could reduce crop yield or potentially ruin a whole field of crops. Citrus Canker is a common disease among citrus fruits around the world mainly in the Americas and Brazil (Wikipedia, 2019).It is caused by bacteria known as Xanthomonas axonopodis pv. citri and Xanthomonas axonopodis pv. Aurantifolii. (Gottwald, 2005) Citrus plants, that encounter water or wind that carry the bacteria, in the early stages of its life will end up with citrus canker. This is shown by lesions in the leaves that appear as yellow halos on the fruit. (Gottwald, 2005) It is possible through gene-editing to make citrus fruits resistant to this disease. By targeting the CsLOB1 gene, which is responsible for the promotion of canker development in citrus, it is possible to make said fruits more resistant than their wild variant (International Service for the Acquisition of Agri-biotech Applications, 2019).There aren’t inherently resistance genes within citrus fruits due the high amount of heterozygosity, which is where two different alleles are found at a single locus (Allendorf & W., 2014). Consequently, it is much more difficult to breed resistant oranges. These plants tend to have a gene that will cooperate with a pathogen to increase pathogen growth and symptom development within the fruit itself these are what are known as susceptibility genes and are present in most plants. (Aihong, et al., 2017)By altering the susceptibility gene CsLOB1 it is possible to make a heterozygous citrus fruit that is resistant to the bacteria thus it will be resistant to the actually citrus canker disease. As a result, it reduces a lot of stress of losing the fruits and increases yield as almost all the fruits will make it to harvest as they won’t be infected by the canker.

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Abiotic stress plays a key factor in the growth and yield of crops. Certain crops can only grow in certain climates such as maize plants only able to grow in temperate climates like Europe. However, with world population increasing particularly in tropical countries and climate change making temperatures higher, (Clarke & Zhang, 2013) it is ever so important to find ways to grow plants in unstable and often unpredictable climates. Plant flowering is a response to photoperiod censoring and as such in certain climates, certain plants cannot grow. (Soyk, et al., 2016) Altering the gene responsible for this can determine how fast a plant can grow and where it can grow. In the case of tomatoes, it was discovered through quantitative trait locus mapping in inbred populations that SELF PRUNING 5G (SP5G)plays a major role in influencing daylight adaption in tomatoes. (Zhang, et al., 2018)Flowering is what actually produces the tomato fruits in this case as it is transitioning from vegetative growth to the reproductive growth and as a result this is the kind of growth that we want to be sped up. (Bäurle & Dean, 2006) There are 2 main types of plants, Long Day plants (LD) and Short Day plants (SD) LD plants flower when daytime is long and SD plants flower earlier. (Takato & A., 2006)By making the tomatoes SD plants by altering the gene, it is possible for them to grow in tropical climates as the flowering process is sped up thus offering a crop not local to the area, to the area.

CRISPR raises one major issue despite all its positives and applications in agriculture and that is the ethics behind it. It is often considered unethical to alter the genetics of an organism and this can pose issues as this needs to be detailed on packaging and as such people can tend to steer away from GM crops as they would prefer a more natural crop. As such this can lower profits. There is also a moral issue in that a lot of countries that would actually require the GM crops to help them either do not have the money for the technology or the reach within their own country to provide the food to everyone (Carolyn & Mazhar, 2019)

In summary, CRISPR Cas9 can benefit many different fields of the agricultural industry. Making crops larger or tastier can serve as a bolster to popularity and can also make the crops more cost effective thus making them more accessible. The process itself by which to do this isn’t very difficult if the required equipment is available. Development of disease resistance in plants highly increases yield without altering the taste of the desired crop moreover it mains that any medication that would have been used to prevent the diseases would not need to be used thus preventing any form of external contamination. This process is also very easy to perform however finding the specific susceptibility gene can be particularly difficult but does tend to end up paying off. Editing genes to make crops grow better in certain disadvantageous environments has the potential to make them more accessible to other parts of the world altering the SP5G gene also allows for plants to potentially grow faster which in turn increases yield. Moral and ethical reasons tend to hinder the progress of CRISPR uses elsewhere but doesn’t really have a major impact in the agricultural industry as it is very closely monitored, and a lot of testing must happen before anything can be released to the public. CRISPR is still in its infantile stages but shows limitless potential and could provide even more benefits for the agricultural industry.