In a world under pressure from climate change, CRISPR-edited crops could be the future.
Writer: Alice Ho
Editor: Maria Stoica
Artist: Lucie Gourmet
In many science fiction blockbusters, gene editing has been responsible for creating some of our most beloved superheroes and supervillains. But what if we have to use it on plants ‒ and not on humans ‒ to save our planet?
Recently, the 2020 Nobel Prize in Chemistry was awarded to scientists Jennifer Doudna and Emmanuelle Charpentier for their work in developing the revolutionary gene-editing tool CRISPR/Cas9, popularly referred to as CRISPR. The technology has been mired in controversy, with many questioning its possible side effects and potential to propagate eugenic ideals (through genetically engineered ‘designer babies’, for one).
Nevertheless, CRISPR is also highly promising ‒ scientists can now edit plant genomes with unprecedented precision, creating safer and cheaper products than previous gene modification techniques. Hence, CRISPR is being used in the hope of tackling one of mankind’s most pressing issues: climate change.
The United Nations has named climate change “the defining issue of our time”. It’s not difficult to see why ‒ on top of the 821 million people already undernourished, modelling by the Intergovernmental Panel on Climate Change predicts that a further 1 to 183 million will be at risk of hunger due to climate change. Scientists are thus investigating how CRISPR could provide a solution to food insecurity.
First, we must examine CRISPR’s fundamental function. CRISPR/Cas9 has two components: CRISPR and Cas9. In nature, they act together as a ‘search and destroy’ mechanism that allows bacteria and archaea to defend themselves against intruders. CRISPR, a type of DNA, encodes RNA sequences that ‘search’ for and pair with complementary DNA of invading viruses and plasmids. Cas9, a protein, then cleaves these foreign sequences, destroying the viral invader.
Scientists manoeuvre these same principles to introduce traits to plants, conferring additional resilience towards climate change. First, they identify the target gene which produces the desired trait, such as drought resistance, and reconstitute it in RNA. This ‘guide RNA’ is inserted into a cell together with Cas9, where it binds to the target gene and allows Cas9 to cut through both strands of DNA. A new DNA sequence can be introduced at the same site. Finally, the guide RNA and Cas9 are removed. To pass on the new desired trait, the mutant plant can be crossed with a native plant, producing a new strain of improved crops.
Currently, global food security faces several threats. Estimates show that by 2100, around 50% of insects, mostly pests or disease vectors, will shift ranges by about 50%. As the distribution of pests and diseases change, many crops are failing to adapt and are becoming devastated. One such crop is Theobroma cacao, commonly known as the cocoa tree.
Imagine Valentine’s Day without chocolate truffles or Christmas without hot chocolate. This could soon become a reality if we are unable to stop the myriad of diseases ravaging cocoa plantations. Thankfully, scientists are looking at CRISPR for a solution. In cacao plant tissue, CRISPR has been used to delete the TcNPR3 gene, which suppresses the plant’s immune response against pathogens. While ongoing research is still testing this method in whole plants, it could ideally increase the resistance of cacao to diseases that would have previously wiped out entire farms of fruit. Similar techniques have been used in laboratories to make wine grapes, bananas and papayas more resilient to mildew, fungi, and insect-pests, respectively.
Furthermore, abiotic factors such as rising temperatures and changing precipitation patterns are significant stressors to food crops. By increasing plant tolerance to stressors, CRISPR could be key in helping plants adjust to adverse environmental conditions, so that we can maintain our food supply and continue to enjoy the foods we love.
In addition to making agriculture durable, CRISPR is also being used to make agriculture more sustainable. Since 1961, the use of nitrogen fertilisers has increased by about 800%, polluting soils and waterways with nitrogenous waste. As a result, researchers are considering how CRISPR can decrease our dependence on them. Start-ups such as Pivot Bio are engineering microbes that can replace the harmful fertilisers. Other research explores the use of CRISPR to enhance the abilities of nitrogen-fixing bacteria in plants, which convert nitrogen in the soil into a form that plants can process.
To lower greenhouse gas emissions from the agricultural sector, one research team is using CRISPR to develop an improved grass species which makes cows burp less ‒ and thus produce less methane. Over at the Salk Institute, the Harnessing Plants Initiative is taking a different approach. It aims to create ‘ideal plants’, which can absorb more carbon dioxide from the atmosphere as they grow and release less carbon dioxide when they die. Researchers are manipulating genetic pathways that allow plants to grow bigger and more robust root systems, so that they can store more carbon dioxide in soils.
CRISPR-edited crops are estimated to hit the shelves in about 5 to 10 years, and the possibilities are certainly exciting. However, CRISPR isn’t the silver bullet to all climate change-related agricultural issues. More mundane forms of action such as converting to veganism and reducing consumption and waste are equally important in deciding our planet’s fate. CRISPR still has a lot of rough edges, including potential side effects, inadequate ethical guidelines, and uncertainties about its effectiveness in practice. Until these are ironed out, we will have to wait before the application of this technology becomes the norm.