While some parts of Europe are ravaged by floods, other regions are suffering from desertification and water scarcity. How can more drought-tolerant plants help? Hannes Kollist, Professor of Molecular Plant Biology at the Institute of Technology, University of Tartu, gives an insight into those questions.
The interview was first published in the Life in Estonia Autumn 2023 issue.
Professor Kollist, you breed drought-tolerant plants at your institute. How did you get into this field?
We are curious to understand which proteins and genes regulate specific processes in plants. We are focused on studying the immediate reactions through which plants sense changes in the environment. Plants become stressed when conditions are no longer optimal for growth. Ideal growth requires about 25 degrees of heat, enough light, sufficient water and basic nutrients.
One of the quickest ways to respond to environmental changes is to open or close stomatal pores on the surfaces of plant leaves. In order to stay alive, a plant opens its stomata to let in atmospheric carbon dioxide. For plants, CO2 is a staple food that is converted into sugars and other energy-rich molecules through photosynthesis. In order to absorb CO2, plants open up stomatal pores, but this also means that water evaporates. In the leaf, the humidity is usually somewhere near 100 percent because all cellular activity takes place in a moist environment.
Opening and closing the stomata is the quickest way for a plant to protect itself against wilting or drought. We looked at the mechanisms of opening and closing the stomata. In particular, we were interested in how plants respond to changes in the concentration of CO2 in the air. We investigated which genes and proteins regulate the stomatal opening and found that CO2-related regulators influence overall water loss via stomata. When we altered certain regulators, we got a plant with more closed stomata, and therefore a more drought-resistant plant. This has been a global question for plant biologists: to understand how plants sense changes in CO2 concentration and use this for manipulating its water-loss and CO2 uptake.
Jointly with colleagues from the US and Japan, we managed to provide an answer to the ultimate question – how is CO2 sensed in the guard cells? This sensor is important for plant water management but also affects CO2 fluxes globally. CO2 emissions caused by humankind are about 9 gigatonnes, whereas annual terrestrial CO2 uptake via stomatal pores is around 120 gigatonnes.
How much drought-tolerant plant breeding is going on in the world?
More and more these days. The regions where food production has largely been concentrated – America, Spain and Italy – are now facing the most severe situation due to climate change.
This is not a very simple question because, for example, in the case of a plant disease, you can find the resistance genes and mechanisms, transfer them and get a resistant plant relatively quickly. Drought-tolerance is a much more difficult trait because the plants we have created have more closed stomata all the time, but in the case of our tomatoes, for example, we haven’t seen any negative effect on yields. This tomato uses significantly less water, but the yield doesn’t change.
What did it take to create water-saving tomatoes?
Tomatoes seem to be extremely plastic plants that consume however as much water they have available. We looked for genes and proteins that regulate CO2 sensing in the guard cells and found protein kinases. If you want to know about any regulators, do some screening. If you have a population with very high genetic variation (for example, mutagenised seeds or different ecotypes of the same plant), you look for individuals of interest based on a given trait.
In our case, this was determined by searching plant lines that did not respond to CO2, and we used self-built instruments to measure this. We found out which gene had mutations, and that’s how we came up with proteins that regulate the perception of CO2, which we can modify as needed: to make the stomata more closed or more open.
Ketchup tomatoes are mostly grown in the field, and it is important that they use as little water as possible. In contrast, so-called eating tomatoes are mainly grown in greenhouses, where conditions are optimised, often CO2 concentration is doubled to maximise photosynthesis, humidity is high and thus water-saving is not critical. In such conditions, desired tomatoes should rather have more open stomata that do not close in response to elevated CO2. We have technology to make such plants as well now, and we are working on having such tomatoes as well. We are using the same methods for adjusting barley water-use characteristics as well; the first barley lines will be tested this autumn.
How far along are you with drought-resistant tomatoes? Could it be on the market soon?
In principle, yes. We’ve done growth tests and measured acidity, sugar content, lycopene etc. in these fruits. We haven’t gotten to a classical variety comparison yet, which would need to be done in larger agronomic-scale greenhouses. Furthermore, we would like to carry out these tests jointly with the Estonian Centre for Rural Research and Knowledge, but then we received a letter from the Ministry of Climate saying that our plants were being considered as GMOs.
I think it would be unrealistic for us to go ahead with applying for getting authorisation of experiments with GM-plants according to current EU rules, which are simply overwhelming, even for big companies. I think we could try these tomatoes in real production. In our tomatoes, only two proteins have been disrupted, so we have not introduced any foreign DNA.
Now more sensible winds are blowing in the EU and perhaps the introduction of these types of changes will be taken off the GMO Directive. In fact, the EU should also change the GMO directive altogether, as it is in serious conflict with scientific findings.
As meat production creates a huge environmental footprint, could a more widespread shift to vegetarianism help save the planet?
It certainly would. Almost 40% of land is used for agriculture, of which two-thirds is used to feed these animals that we eat and only one third is used for cereal/vegetable/fruit production. Livestock farming also produces methane, which is a greenhouse gas nearly 100 times stronger than CO2. Thus, eating less meat helps make our societies more sustainable and climate friendly.
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