More than 2 billion people worldwide suffer from malnutrition. Not because they are getting too few calories, but because their food contains insufficient essential minerals like zinc and iron - the phenomenon of ‘hidden hunger’. Together with colleagues from Denmark and Portugal, researchers from Wageningen University & Research have discovered how plants recognise that they are not absorbing enough zinc, and how they can improve the zinc intake by plants. The first experiments with this led to a 50% increase in the zinc content of seeds. This discovery can make an important contribution to solving the ‘hidden hunger’ phenomenon in the world.
Potentially good news for malnourished people worldwide
Deficiencies of zinc and other essential minerals and vitamins is one of the leading causes of malnutrition worldwide. It is estimated that more than two billion people suffer from zinc deficiency, a problem that can lead to a weakened immune system, lower IQ and impaired growth. This form of malnutrition can be caused when people live on crops grown on relatively infertile farmland, with naturally low levels of zinc, meaning that zinc levels in staple crops such as rice, wheat and maize are also low.
But suppose you could flip a switch in crops that would increase their uptake of zinc, iron, or other nutrients, so they absorb more nutrients than they would otherwise. Researchers from Wageningen University & Research, in collaboration with colleagues from the University of Copenhagen and the University of Porto, have found that ‘switch’ for zinc uptake in the thale cress (Arabidopsis thaliana). A publication on this subject recently appeared in Nature Plants.
“It has been shown for the first time that, by using a molecular ‘switch’ in the plant, we can ensure that the plant takes up more zinc than it would otherwise, without obvious negative consequences for the plant”, explains Mark Aarts, Professor at the Laboratory of Genetics at Wageningen University & Research and co-author of the publication.
Plants store 50 percent more zinc in seeds
Zinc is important to our health because it helps maintain a large number of chemical processes and proteins in our bodies. When these processes stop functioning properly, we easily get ill. Zinc is also essential for plants, and the absence of zinc has particularly detrimental effects on growth and development.
Researchers have long been trying to understand how plants regulate their zinc intake. The research by WUR and the University of Copenhagen has now identified the first two proteins in plants that act as zinc sensors and determine the ability of the plant to absorb zinc and distribute it through the plant.
By slightly modifying the properties of these sensors, or molecular 'switches', which control a tightly connected network of zinc transporter proteins, the researchers have managed to get plants to absorb more zinc: “This adjustment gave thale cress plants the signal that they were permanently zinc deficient. This kept the plant's mechanism for zinc uptake active, and resulted in an increase in zinc content in the seed by as much as 50 percent compared to normal plants.”
Next step: rice, beans and tomato
The researchers have demonstrated that it is possible to increase zinc-absorption in their model plant, but the next step is to reproduce the results in real crops. And they are already well on their way to doing so. Currently, the experiment’s results are being repeated in bean, rice and tomato plants. “If that succeeds, we will have interesting opportunities to develop more nutritious crops with biofortification”, Aarts said. He believes that biofortification is a sustainable solution to improve the micronutrient content of our food.
“Now that we know which genes are key for this, it is possible to conduct targeted breeding based on this trait. It would be even faster if specific gene editing with CRISPR-Cas could be applied. At the moment, strict regulations make this difficult in the EU. However, outside the EU where the issue of ‘hidden hunger’ is most pronounced, there are several countries that are open to such an approach. With new varieties that store more zinc in their seeds, crop yields can increase and so can the nutritional value of the products made from them.”
- Zinc is a key structural and catalytic component of a large number of proteins. For all proteins to function properly, an optimal zinc supply needs to be maintained, avoiding deficiency or toxicity.
- In humans, the risk of zinc deficiency can lead to growth impairment, immune dysfunction, and cognitive impairment.