Nov. 8, 2019
Supporters of genetic engineering have long promised it will help meet the world’s growing demand for food. But despite the creation of many genetically modified (GM) pest- and herbicide-resistant crops, scientists haven’t had much success with boosting crop growth. Now, researchers have for the first time shown they can reliably increase corn yields up to 10% by changing a gene that increases plant growth—regardless of whether growing conditions are poor or optimal.
“It’s incredible,” says Kan Wang, a molecular biologist at Iowa State University in Ames who was not involved in the new study. Aside from increasing corn harvests, she says, the new modifications should inspire other researchers in the quest for coaxing higher yields out of other crops.
The world’s most widely planted GM crops, including soybean, corn, and cotton, were created with a few relatively simple genetic tweaks. By adding a single gene from bacteria to certain crop varieties, for example, scientists gave them the ability to make a protein that kills many kinds of insects. Another simple genetic manipulation results in crops that withstand glyphosate or other herbicides; one benefit is that farmers can kill weeds without eroding the soil. Yet another protects crops during drought. But it’s been a lot harder to come up with plants that also yield more grain in good conditions, because of the complex genetics involved in plant growth.
Starting in about 2000, companies around the world began to screen in earnest for single genes that could increase yield. Only a few identified genes have shown promise, and many companies have reduced or stopped screening for genes related to crop yield, because of the low rate of success.
But researchers at Corteva Agriscience, a chemical and seed company based in Wilmington, Delaware, decided to look at genes that function like master switches for growth and yield. They picked MADS-box genes, a group common in many plants, before settling on one (zmm28) to alter in corn plants. The challenge of working with genes that regulate development is making sure they turn on the right amount at the right time and in the right type of tissues. “It’s awfully easy to get messed up plants” if the genes are too active, says Jeff Habben, a plant physiologist at Corteva who helped lead the research.
The group aimed to fuse zmm28 with a new promoter, a stretch of DNA that controls when the gene is activated. After trying a dozen, they found one that worked reliably. Usually, zmm28 turns on when corn plants begin to flower. The added promoter turned on zmm28 earlier than happens naturally and also continued to boost the gene’s beneficial effects after flowering. “If you make the gene work harder and longer, you can make the plant perform better,” Wang says.
The researchers tested the enhanced gene’s performance in 48 commercial types of corn, known as hybrids, that are commonly used to feed livestock. In field tests across corn-growing regions of the United States between 2014 and 2017, they found that the GM hybrids typically yielded 3% to 5% more grain than control plants. Some yielded 8% to 10% more, the team reports this week in the Proceedings of the National Academy of Sciences. The benefit held regardless of how good or bad the growing conditions were. “This is one of the best examples where GM for yield actually works convincingly in a field environment,” says Matthew Paul, a crop scientist at Rothamsted Research in Harpenden, U.K.
The increased growth is due to several factors. First, the engineered plants have slightly bigger leaves, which are 8% to 9% better at turning sunlight into sugars. “This increase is really a big deal,” says Jingrui Wu, a plant physiologist at Corteva, because photosynthesis has been difficult to improve with genetic engineering. The plants are also 16% to 18% more efficient at using nitrogen, a key soil nutrient—another trait that has been difficult for plant breeders to manipulate because of complex genetics.
“This looks very promising from a commercial point of view,” says Dirk Inzé, a molecular biologist at VIB, a research institute in Flanders, Belgium. Corteva has already applied to the U.S. Department of Agriculture (USDA) for approval of new higher-yielding hybrids. (Although zmm28 and its promoter occur naturally in corn, they were paired using a technique that USDA regulates as biotechnology.)
Habben estimates it will take 6 to 10 years to gain formal approval in countries around the world. There’s a “good chance” that related regulatory genes might boost yield in other cereals, Inzé says. The large-scale field demonstration in corn “reinforces our belief that intrinsic yield can be improved if we do it cleverly,” Wang says. “This indeed will give people inspiration.”
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