Researchers bioengineer soybean plants to increase yield (CEP)

Published in the September 2022 print issue of Chemical Engineering Progress (CEP), the flagship publication of the American Institute of Chemical Engineers.

I am a contracted freelancer for CEP, with 1-2 articles published each month.

In the agricultural state of Illinois, researchers have bioengineered soybeans with higher photosynthetic efficiency. It could lead to more crop production using fewer land resources, which may provide food security to the world’s poorest.

Projections show that global food supply is not increasing fast enough to meet demand. “Getting more crop yield off of the same piece of land is so important,” says study author Stephen Long of the University of Illinois at Urbana-Champaign, “because it means that, a) we’ve got insurance against further shortages of food, and b) if we don’t need that food, we can let the land go back to nature.”

Improving photosynthesis has been Long’s research focus for the past fifty years. The new soybean study is built off a decade of work in which his team figured out how to optimize bottlenecks in the photosynthesis process.

“In this particular case, one bottleneck that we worked out was crop canopy—leaves going in and out of shade all day long,” says Long. This intermittent shadowing naturally occurs as a result of wind, cloud cover, and the sun moving across the sky.

During photosynthesis, more sunlight does not generate more biomass. In fact, too much light will produce reactive oxygen species that act similarly to bleaches. Without a built-in photoprotection method, this would destroy a leaf. 

Plant evolution has dealt with this by inducing a mechanism called non-photochemical quenching. Similar to a release valve, it takes excess energy from direct sunlight and harmlessly dissipates it as heat. 

The problem, Long and his research team found, is that when the leaf moves from sunlight into shade, non-photochemical quenching takes a few minutes to relax, or stop. While the plant is in shadow, precious energy that could be used for photosynthesis continues to be lost.  

In a 2016 landmark study on tobacco plants, Long and his team discovered a method to speed up the relaxation rate of non-photochemical quenching, resulting in higher crop yields. The soybean study applies the same bioengineering technique, with similarly promising results. 

The method works by up-regulating three genes, VDE, PsbS, and ZEP, which are known to influence non-photochemical quenching. As a result, the photoprotection mechanism is accelerated. When the plant is in the sun, it induces more rapidly; in the shade, it relaxes more rapidly. This saves energy to produce more biomass.

To test the effect on yield, the researchers ran two field experiments in Illinois with multiple lines of transgenic soybeans. In the 2020 trial, five showed a significant increase in seed yield, and none showed a lower output. 

Overall, the bioengineered soybeans averaged a 24.5% improvement in yield compared to wild types, with no effect on nutritional value. “That is huge as far as crossbreeding goes,” says Long.

In 2021, however, the transgenic soybeans did not produce a higher yield than wild types. Long explains the difference with variations in weather conditions.

A severe windstorm hit right before a critical period of flowering, which blew over crops and left the lower canopy completely shaded. Accelerating non-photochemical quenching is only beneficial when plants experience fluctuations in light.  

Still, in the upper canopy, the rate of relaxation was 11 to 23% faster than wild types. “We could see from our photosynthesis measurements that it was working, although we did not see a higher yield,” says Long. 

Next, the researchers will continue to trial their transgenic soybean lines in different climate and geographical conditions. They envision that the same bioengineering method could be expanded to other crop plants, such as cassava or cowpea, which are relied on in parts of Sub-Saharan Africa and South Asia.

“According to the Food and Agriculture Organization of the United Nations, over 800 million people are starving right now in the world. That’s one in ten,” says Long. “We need to be doing everything possible that we can to get seed that will produce more.”

De Souza, A. P., Burgess, S. J., Doran, L., Hansen, J., Manukyan, L., Maryn, N., Gotarkar, D., Leonelli, L., Niyogi, K. K., & Long, S. P. (2022). Soybean photosynthesis and crop yield are improved by accelerating recovery from photoprotection. Science, 377(6608), 851–854. https://doi.org/10.1126/science.adc9831