The Future of Food: Plant science approaches to the global challenge of food security
by James Turner
By 2050, it is expected that the world population will reach 10 billion. The amount of food necessary to feed our appetites is expected to rise by 50%, and as things stand it is impossible for our current methods of agriculture and plant production to sustain this rapid population growth.
Fortunately, scientists at the University of Sheffield, under the banners of the Institute for Sustainable Food and the Grantham Centre for Sustainable Futures, are using their knowledge of fundamental plant processes to research new approaches to sustainable food production.
At the core of all this research is a key notion: if we are to ensure that plant production is sustainable, we must first ensure that plants' basic needs are met.
Reducing stomatal density to combat water scarcity
We started by looking at stomatal genes to see what would happen if we altered some of them. We found that when we knocked one of those genes out it caused the leaves to generate more stomata.
Professor Julie Gray
Like animals, plants need food. However, they 'eat' in a very different way – by using carbon dioxide (CO2) and sunlight to create sugar. The stomata – tiny pores found in the epidermis of leaves – facilitate the gas exchange in plants, taking in CO2 from the atmosphere and releasing water vapour.
This release of water vapour isn’t a problem in water-rich environments, but can be devastating in drier soil. As global temperatures rise and more crops are grown, the drier our soil becomes. Rainfall is becoming less predictable and water is often scarce.
To combat this scarcity of water, Julie Gray, Professor of Plant Cell Signalling at the University of Sheffield, and her team have been looking into the effect of reducing the number of stomata in several plants, including wheat, rice, barley, and Arabidopsis (thale cress), often referred to as the lab rat of plant biology.
"We started by looking at stomatal genes to see what would happen if we altered some of them," said Julie. "We found that when we knocked one of those genes out it caused the leaves to generate more stomata. So we concluded that this gene was crucial in controlling stomata number."
With the plants modified so that they have varying numbers of stomata, Julie’s team test their ability to thrive in various different environments. They do this by using the Sir David Read Controlled Environment Facility, Sheffield’s state-of-the-art climate control centre, which allows researchers to create virtually any future climate right here at the university.
So far, they have found that reducing the number of stomata can actually benefit certain plants in most future climates. As water runs low, the reduced number of stomata allow the plants to retain what water there is for longer while still taking in enough CO2 to stay healthy and flourish.
Julie has begun to expand her work from Arabidopsis to wheat, rice and barley, but says that it's necessary that farmers get involved in this research for it to really make an impact on agriculture.
Understanding how C4 photosynthesis converts CO2 more efficiently
Another way in which plant production can be made more sustainable is by making the way plants convert CO2 into energy more efficient. More than 90% of plants use C3 photosynthesis to create sugar from sunlight and CO2. However, some plants have evolved to use C4 photosynthesis, which concentrates CO2 inside the leaf and makes photosynthesis more efficient in hot, sunny climates.
Professor Colin Osborne researches how C4 photosynthesis evolved in wild plants and how this has changed their biology. He was also a founding Associate Director of the Grantham Centre for Sustainable Futures, a multi-million pound initiative co-funded by the Grantham Foundation for the Protection of the Environment to bridge the gap between lab-based sustainability researchers and the policymakers responsible for our planet’s future.
So far, Colin has found that as well as greatly improving plants’ ability to photosynthesise by concentrating the CO2 in their leaves, plants using C4 photosynthesis also develop more roots, which could improve their ability to absorb water from dry soil.
The team also recently discovered that plants using C4 photosynthesis, which usually flourish in very hot climates, are also quicker to colonise cold areas, meaning that the benefits of C4 photosynthesis may be even broader than originally thought.
Colin works closely with Sheffield colleagues Professor Paul Quick and Professor Richard Leegood, who are involved with the C4 Rice Project – a multimillion-pound initiative funded by the Bill and Melinda Gates Foundation. The goal of this project is to use genetic modification and gene editing techniques to introduce C4 photosynthesis into rice in order to boost its growth.
"When the C4 Rice project began, there were big gaps in our knowledge of how C4 photosynthesis works," said Colin. "Our work has contributed to the understanding of how C4 photosynthesis evolves in nature, and one of the major lessons learned is that C4 doesn't evolve from typical C3 species, but from C3 plants that already have lots of the characteristics needed to become C4. Rice isn't one of these species, and so the big challenge will be how to modify the rice leaf to make it much more C4-like."
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A combination of optimising stomata number and modifying plants to use C4 photosynthesis would have a massive impact on plants’ productivity, with a 50% productivity increase coming from C4 photosynthesis alone, and Julie’s rice plants maintaining the same yield with 40% less water.
Helping plants fight off pathogens through epigenetics
However, productivity is not the only problem. Plants still need to protect themselves from harmful pathogens, just like animals, and using pesticides becomes harder and harder as the number of crops increases.
This is key challenge for Professor of Plant Environmental Signalling, Jurriaan Ton. His research focuses on improving plants’ immune systems so that they can deal with pathogens and other threats by using traits inherited through epigenetic modifications, rather than relying on pesticides.
Epigenetics is quite hard to define, but Jurriaan refers to epigenetic traits as those that are stable, heritable, and cannot be explained by variation in DNA sequence.
Unlike genetic modifications, which occur due to a change in the genetic sequence code of DNA, epigenetic modifications don't change the sequence code at all. Instead, they involve biochemical modifications to the DNA or the proteins associated with the DNA (collective referred to as the chromatin).
Some chromatin are packed very tightly, others less so, giving rise to differences in the transcription or transcriptional responsiveness of genes. This means that genes in very tightly packed chromatin are often not expressed, whereas genes in very lightly packed chromatin can be expressed to much higher levels. These changes cause plants to become phenotypically different (have different physical characteristics), while remaining genotypically identical (have the same genetic code).
Furthermore, these epigenetic modifications can be passed to the plants’ offspring, meaning that they too have an altered phenotype despite the fact that their genotype remains the same. The extent to which these epigenetic traits (which can be reversible) have implications for evolutionary theory is becoming a much debated subject in plant biology. There have even been calls for change to the 100-year-old evolutionary theory in response to these discoveries.
Though such work can be done through genetic modification, epigenetic modification may well function as a quick, alternative way to improve desirable traits in elite crop varieties without having to resort to genetic modification. Crops with high yield can maintain the genetic code that allows for this yield, yet can be altered epigenetically to weather the storm of pathogens more efficiently.
We’ve been working with partners in the Netherlands, France, and Germany to study Arabidopsis over many generations, and we’ve yielded lots of interesting results.
Professor Jurriaan Ton
The need for durable disease resistance in crops is especially important considering the current dramatic rates of climate change. As global temperatures rise, new pathogens begin to thrive, some of which will be devastating to crops. Moreover, though pesticides can effectively protect crops, the carbon footprint of producing and applying pesticides is far higher than that of simply breeding modified crops, making modification the greener option.
So far, most of Jurriaan’s work has revolved around modifying Arabidopsis, as it is one of the easiest plants to modify, and his lab has already begun to translate the proof-of-concepts to crop plants, such as tomato and maize.
"We’ve been working with partners in the Netherlands, France, and Germany to study Arabidopsis over many generations, and we’ve yielded lots of interesting results showing how epigenetic traits, specifically those relating to improving disease resistance, are passed on through generations and don’t affect growth," said Jurriaan.
Next steps in food security research
Solving a problem as complex as food sustainability is not simple and requires collaboration. This is why Sheffield’s Institute for Sustainable Food and the Grantham Centre for Sustainable Futures bring together scientists from across the university to work on sustainability solutions together, which range from the purely scientific to the political.
In ten years’ time, we may begin to see the new ideas of today appearing for the first time in farmers' fields. This is why we need young researchers now.
Professor Colin Osborne
"We can translate our work from Arabidopsis to crops without any real trouble, but being able to move this from the lab to a stage where people will actually eat the crops is a big challenge,” said Julie. “That’s why we need industry partners and why the institute is so important. It brings in people who know more about the market than we do and allows us to share our findings with them."
Researchers from both centres are also calling for more bright young people to further their work. But what does this next generation of scientists have to look forward to?
The once controversial field of epigenetics is really starting to find its feet, and as a relatively young field of study, it still has lots to offer future scientists. Thanks to a resurgence in plant and crop sciences, our understanding of the fundamental workings of plants and their genes is also continuing to grow, and Julie, Colin, Jurriaan, and the rest of the institute and the Grantham Centre hope to see this growth translate itself into crop sciences very soon.
"In ten years’ time, we may begin to see the new ideas of today appearing for the first time in farmers' fields," said Colin. "This is why we need young researchers now to develop expertise in plant science, understand the issues of sustainability, and train with the skills needed to join plant research labs."