Food crops are major sources of nutrients and are considered staples in many developing countries. For example, 90% of the rice we have caters for almost half of the world's population for it is widely consumed in East Asian countries (notably China).
However, due to the ever-growing global population and the effects of human-driven climate change, the scarcity of food continues to be a global issue. Not to mention, this rising demand is unlikely to be met if one were to continue to employ existing agricultural methods. Therefore, using genetic engineering as a tool to boost crop yield or even create transgenic plants with enhanced nutritional content has become a hot topic in our world today.
In this article, we will be talking about genetically modified plants, their production process, as well as the risks and benefits that they carry as we attempt to use them to strengthen our food security and health.
This is not a new concept
Selective breeding
Genetic modification has been widely used by humans for millennia to consistently improve the appearance, taste, and growth of the many plants that we grow for food. Consequently, our fruits and crops today look very different from the ones from a couple of hundred years ago and are almost unrecognisable when compared to the first wild variants. This was essentially achieved by choosing plants with the most favourable traits and then selectively breeding them (See Figure 1).
Although selective breeding is still practised in our world today, there are a few major shortcomings of this technique that call for a different approach.
For instance, it can take up to decades to even make viable modified crops! The reason behind this is due to the unpredictability of the genes that get inherited by the offspring. Essentially, the DNA of both parents can be assigned randomly. As a result, genes encoding for desirable traits (e.g. those encoding for resistance to pathogens) could get bundled with genes encoding for poor quality traits.
Figure 1: Selective breeding is a conventional breeding practice to produce crops with selected and desirable properties. To begin with, plant breeders will select two parents with beneficial traits - for example, one would be resistant to viral infections whilst the other one would be larger in size - with the intention of reproducing offspring crops that are bigger and are also virus-resistant. However, it is common for some offspring to carry only one of the desired genes, and the reason for this is because random recombination of genes between chromosomes of its parents can happen. As a result, the new offsprings can carry beneficial genes blended with less desired ones from each parent. This figure was adapted from The Royal Society (2016)’s How does GM differ from conventional plant breeding?.
Genetic engineering
In contrast, genetic engineering - another form of genetic modification - directly changes a specific region of the plant’s genome by inserting a foreign gene from an unrelated organism. Hence, this method removes the need for performing multiple selective cross-breeding, making it a much faster process.
Overall, this technique also leads to the production of genetically modified organisms (GMOs) that have an increased shelf life coupled with new beneficial traits such as the ability to resist biotic and abiotic stresses.
How are genetically-modified crops made?
The classic tactic - recombinant DNA technology
One of the ways we can genetically modify plants is by employing a technique known as recombinant DNA technology.
We begin the process by first isolating the DNA from an organism that carries the desirable gene we need. This is followed by mass-producing the desirable gene by inserting it into bacterial plasmids, and they can then reproduce and make millions of copies of that particular gene. After that, these bacteria are used to infect a small piece of plant tissue (e.g. leaf tissue) so that the desired gene can be introduced to the target plant’s genome. Once that’s done, these cells can be induced to form a fully grown transgenic plant containing the engineered new trait. Consequently, the newly introduced desirable gene is inherited and gets stably expressed over the next generations of plants (See Figure 2).
One species of bacteria frequently used to modify plants is Agrobacterium tumefaciens, a naturally occurring soil bacteria. It gained the title “nature’s own genetic engineer” as they frequently infect plants and cause tumour-like growths by transferring the disease-causing gene from its plasmid into the genome of its plant victim. Eventually, this natural process was exploited by scientists, where they basically replaced the disease-inducing gene with desirable genes so that they can modify plants in a good way.
Interestingly, we have made tremendous progress over the recent years at getting crops to flourish when cultivated in exhausted soils (which, in normal circumstances, would have been a futile effort). This is arguably a big deal because depleted soils are a common by-product of intensive farming and agriculture, and we would usually need the soil to be filled with essential nutrients if we wanted to have a high-quality crop yield.
Figure 2: The process of genetic modification of plants using DNA recombinant technology. Scientists often like to use the plasmids of Agrobacterium tumefaciens to modify plants as these bacteria can infect them and transfer part of their DNA that integrates into the plant genome. To prepare the plasmid for its job, we first use an enzyme to replace the natural disease-causing gene with the desirable gene. As a result, a recombinant plasmid is created because it contains DNA from bacteria and another organism. Following that, this plasmid is used to infect plant tissues. And once the new DNA becomes a part of the plant genome, the cell growth is triggered to generate an entire plant. This figure was adapted from Priyadarshan (2019)’s “Genetic Engineering” and Abhisheka (2020)’s “Applications of recombinant DNA technology”.
CRISPR-Cas system - the new popular tool
Although DNA recombination technology paves a way for considerable progress in improving the overall quality of seasonal harvests, faster and more specific gene-editing tools have been developed over recent years. This, in turn, could be a crucial component to help us meet the growing food demand.
The most promising one is the CRISPR-Cas9 system (an acronym for Clustered Regularly Interspaced Short Palindromic Repeats). This name essentially originated from a long array of repeated sequences found in bacteria, which serves as a vital component in protecting them from invading viruses as well as any future attacks. Meanwhile, Cas9 is a type of enzyme that acts like a tiny pair of scissors by cutting DNA strands.
When it comes to genetically engineered crops, the CRISPR-Cas technique is most likely the gold standard at the point of writing as this technique has the unique ability to cleave specific regions in the genome, allowing the insertion of desirable genes at a chosen location. This makes it a better alternative to existing DNA recombination methods, which insert the desirable genes randomly and thereby risking the disruption of vital genes.
It’s not just about food
Did you know - we can actually modify plants to produce therapeutic proteins such as human monoclonal antibodies that can fight against HIV?
Let’s dive into a few examples to understand the marvels of this biotechnology.
Vaccine proteins made in fruits, for instance, are easy to transport and do not need to be refrigerated. Such edible vaccines are a great alternative to using sterile needles, which can be difficult to source in certain areas. Besides that, this allows for efficient delivery to faraway countries in need. Plus, food crops such as tomatoes are also relatively cheap, so medication can become more accessible to less economically developed countries.
Meanwhile, numerous experiments that were conducted on cancer-prone mice demonstrated the potential of utilising crops in medicine delivery. In particular, scientists were able to create tomatoes containing high levels of an antioxidant called anthocyanin, whereby anthocyanins are natural pigments found within blue- and purple-coloured fruits such as blueberries. Given that they are best known for their role in fighting cardiovascular disease and cancer, tomatoes expressing a lot of these molecules, therefore, are a potential anti-cancer snack. Who knows, we could even convert these modified tomatoes into frequently consumed foods such as ketchup or pizza sauce in the near future so that we can protect the wider population from this dreadful condition.
Are they safe?
Despite having discussed the potential wonders of genetically-modified crops, there is a massive controversy over the perceived safety of these food products. In fact, most European countries have even voted for the total ban on genetically-modified crops. Besides that, the long-standing GMO safety debate has led to the decade-long stalling of some of the most promising genetically-modified crops such as the Golden Rice, which is a food product developed to combat vitamin A deficiency.
Many feared the potential risks of developing allergic reactions to these genetically-modified crops. On top of that, it is really tricky for one to prevent the unwanted spread of genetically-modified crops as natural events such as wind pollination are tough to control. Additionally, some critics expressed concerns regarding the possibility of these engineered plants transferring antibiotic-resistant genes to the bacterial population residing in our gut. Nevertheless, even though this was a legitimate concern to have as such bacteria are already difficult to treat, researchers have not found any evidence showcasing adverse reactions or a significant increase in resistant bacteria after consuming genetically-modified crops.
Technically speaking, we could determine the safety of these food products by performing direct rigorous testing for toxins and/or allergic reactions. However, the ability to finance this area of research is largely dependent upon whether the general public is up for it. And unfortunately, one is likely to face various hurdles with respect to the negative public perception surrounding GMOs, which is often exacerbated by the spread of false information and misleading research. For instance, one study performed in the last decade claimed that genetically-modified crops can induce tumours in mice. This publication, although retracted, has ended up fueling the GMO hysteria.
Why should you care?
Genetically-modified crops have tremendous potential to not only help end world hunger but also deliver life-saving medications to the poorer regions of the world (and therefore contain diseases more efficiently). Other than that, the effects of climate change may soon highlight the need for genetically-modified crops so that we can maintain a steady - if not, greater - crop yield annually despite the changing environment.
The problem, however, is that many countries are reluctant to bring this technology to the next level as many feared that GMOs could cause irreversible damage to animal and human health, our ecosystem, or even dramatically reduce the diversity of plants on Earth. Hence, it is vital for us to carry out rigorous tests on all genetically-modified crops before approving any large-scale agricultural projects.
Author
Huong Giang Nguyen
BSc Biochemistry
Imperial College London
#GMO #recombinantDNAtechnology #CRISPR #cropbiotechnology
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