Plants sometimes catch more sunlight than they can handle. To avoid damage, they dissipate excess energy as heat. If this sun protection is no longer needed, however, the leaves need a relatively long time to switch off this biochemical mechanism again and use less solar energy in the decomposition phase than they actually could.

Stephen Long from the University of Illinois and his team now describe in the journal “Science” how they could speed up the process using genetic engineering. The study shows that soybean plants that have been modified accordingly can capture more sunlight and thus produce more yields on the same area without artificial fertilizers.

That could help solve a difficult dilemma: on the one hand, according to the United Nations, the world population is growing by 66 million every year. On the other hand, experts are largely in agreement that the areas under cultivation cannot be expanded further worldwide because this would be at the expense of the existing natural areas. Can genetically modified soybean plants help resolve this dilemma?

“The results presented are still close to basic research,” says Ralf Wilhelm from the Julius Kühn Institute (JKI) in Quedlinburg, commenting on the study, in which he was not involved. However, looking at the biochemical mechanism known as photosynthesis, which uses energy from sunlight to produce biomolecules from water and carbon dioxide, seems promising: “Several research groups are working in this field,” explains Wilhelm.

Stephen Long’s team focused on protecting the plants from the sun because too much sunlight creates reactive oxygen, which can disrupt photosynthesis. To prevent this, enzymes are activated in plants within a few minutes, which open a kind of screen that dissipates excess energy as heat.

But solar energy is wasted in the process. In the forest of leaves of plants growing next to each other like in a soybean field, the uppermost leaves are constantly in the sun, while in the green below, light and shade from leaves growing higher up change relatively frequently. Therefore, the slow degradation of sunscreen can significantly reduce the effectiveness of photosynthesis.

To prevent this, Stephen Long and his team set specific switches in the genome of soybean plants so that the parasol opens and closes much more quickly. A very similar experiment with tobacco plants had already shown that this significantly increases the effectiveness of photosynthesis. Something similar happened with the genetically modified soybean plants and thus with the world’s fourth most important crop product and the most important supplier of vegetable proteins.

In 2020, five of the eight soybean varieties studied with accelerated enzymes produced, on average, about a quarter higher yields than unmodified soybean plants. The plants produced more seeds, the oil content of which was unchanged. Overall, this meant a significantly improved harvest for five lines. However, this success in cultivation could not be repeated in 2021. The modified soybean plants did not provide significantly increased yields.

“Even if this success is not sweeping, further research in this area is worthwhile,” says Wilhelm, interpreting these results. Further experiments should investigate the reasons for the observed significant fluctuations in yields.

There is still a long way to go before such genetically modified soybean varieties can be cultivated, especially since it can take ten years for new varieties to be approved for conventional breeds. There are still unanswered questions: “How do these genetically modified soybean plants behave on soils other than Illinois?” asks Wilhelm. “And what about other climate conditions?”

Genetic modification of plants is severely restricted in the European Union. But European soybean farmers could also benefit from the research: “In similar experiments, markers for improved photosynthesis can be identified, which also show for conventional breeds whether new lines can be expected to produce higher yields,” explains Wilhelm. “In any case, farmers need new varieties quickly that are adapted to climate change and sustainable production.”