Increased soybean yields finally achieved

As many as 828 million people were affected by hunger in 2021, and the number continues to grow. But we can no longer afford to increase food production through agricultural expansion. We need to grow more food on the land already in agriculture by increasing yield. With yields stagnating since the green revolution, new developments via bioengineering provides a means to meet the challenge.

A recent study by Dr. Amanda DeSouza and colleagues has increased the yield of soybean by up to 33%. Soybean is the world’s largest source of animal protein feed and the second largest source of vegetable oil. Although there have been numerous successes in bioengineering soybean to increase soybean yield over the last decade, none have demonstrated these increases in natural field conditions.

Why haven’t bioengineered high-yielding soybean been field tested before now?

Researchers have been using bioengineering to improve soybean for over 30 years. In that time, much of the progress has been in conferring herbicide resistance, although seed quality, pest resistance, salt and drought tolerance, and agronomic traits are also targets. Most of these plants have been tested using greenhouse experiments with plants grown in individual pots.

Bioengineered plant studies are performed in the greenhouse for several reasons. Greenhouses are convenient to access, allow for repeated experiments to be performed throughout the year, and allow researchers to control environmental conditions. On the other hand, field experiments provide limited growing seasons, have little to no control over abiotic and biotic variables, and are time-consuming and expensive to manage. For experiments involving bioengineered plants, researchers must secure governmental authorization that limit and control the release.

Yet it is difficult to extrapolate the results of lab and greenhouse trials to outcomes in the field where plants grow together to form a canopy and experience biotic and abiotic stresses and extreme weather, which affect plant performance and yield. However, this is an important stage because soybean is exclusively cultivated outdoors.

Natural field conditions provided the exact light environment needed to test their bioengineered soybean

Light experienced by plants in the field is very dynamic. When light intensity is too high or increases too fast for photochemistry to use the absorbed light, photoprotection is activated to protect them from damage, allowing leaves to dissipate the excess energy. However, when the leaves are shaded (by other leaves, clouds, or the sun moving in the sky) this photoprotection needs to switch off so the leaves can continue the photosynthesis process with a reserve of sunlight. It takes several minutes for the plant to switch off the protective mechanism, costing plants valuable time that could have been used for photosynthesis.

The authors of the study targeted three genes that code for proteins of the xanthophyll cycle, which is a pigment cycle that helps in the photoprotection of plants. By overexpressing the three genes in soybean using the VPZ construct, the authors were able to accelerate the recovery from photoprotection. When tested in the field, the acceleration gave leaves extra minutes of photosynthesis which, when added up throughout the entire growing season, increased the total photosynthetic rate. This translated to an increase in yield by up to 33% with virtually no change in protein and oil content.

This discovery has been over a decade in the making.

In 2004, co-author Steve Long led a study using model simulations that showed that a delay in the recovery of photoprotection in a multi-layered canopy reduced photosynthesis by up to 30%.

In 2011, co-author Kris Niyogi theorized how a plant’s capacity for photoprotection could be genetically manipulated. In this paper, he suggested the three tested xanthophyll cycle genes as targets.

In 2016, Niyogi’s team demonstrated that nonphotochemical quenching could be induced and relaxed more quickly using transient gene expression of the three xanthophyll cycle genes. Transient expression is the temporary expression of genes, in this case, in a tobacco leaf where the genes were injected.

In 2016, Long and Niyogi’s teams worked together to test the VPZ construct in tobacco. Tobacco was chosen because it is easy to transform, produces a lot of seed, and can be field tested. This work resulted in a 14-21% increase in plant biomass production in natural field conditions.

In 2022, the VPZ construct was tested in soybean grown under natural field conditions resulting in increase in yield by up to 33%.

Will this discovery make a difference to global hunger?

It’s likely that this modification can increase yields in other crops because all plants use these same three genes to regulate non-photochemical quenching. Also, it is technically possible to modify other crops; maize, cotton, potatoes, canola, wheat, rice, strawberries, lettuce, eggplant and many other grains, fruits and vegetables have already been successfully bioengineered and commercialized. In addition, once developed, there is already a precedent for growing bioengineered crops in much of the world. For instance, in 2019, 74% of soybean planted worldwide was genetically modified for herbicide tolerance and insect resistance.

However, there is a lot of research, review and regulation involved in bringing a new bioengineered product to market. According to the Genetic Literacy Project, “in the United States, where much of the agricultural genetic engineering occurs, it takes an average of nearly eight years and the expenditure of more than $135 million to develop a new trait and move it through the regulatory process.”

READ THE ARTICLE:

Amanda P. De Souza, Steven J. Burgess, Lynn Doran, Jeffrey Hansen, Lusya Manukyan, Nina Maryn, Dhananjay Gotarkar, Laurie Beth Leonelli, Krishna K. Niyogi, Stephen P. Long. 2022. ‘Soybean Photosynthesis and Crop Yield Is Improved By Accelerating Recovery From Photoprotection’, Science https://www.science.org/doi/10.1126/science.adc9831