Each year, plant-eating pests account for about 20% of crop losses worldwide.
Growers have relied on what were once considered silver bullet approaches to manage the problem: insecticides and genetically engineered plants. But although both have been successful to a degree, they've failed to fully rein in the problem. Additionally, these methods have stirred a variety of concerns: mounting worry about pesticides' impact on the environment and human health; consumer weariness about eating chemically treated or genetically modified food; and increasing insect resistance to many of the most commonly used pesticides.
That's why a University of Nebraska--Lincoln research team is taking a closer look at an alternative method of pest control that may overcome or mitigate the problems associated with standard approaches. Entomologist Joe Louis and collaborators recently received a nearly $1.2 million grant from the U.S. Department of Agriculture to explore methods of shoring up the natural defense mechanisms of sorghum -- a promising crop for food, feed and fuel -- that would fortify it against sugarcane aphids, a pest that's plagued the plant since 2013.
"Since pesticides remain in the environment and may affect the quality of food, we're thinking in the direction of how alternate approaches can be used," said Louis, Eberhard Professor of agricultural entomology. "That's why we started on developing the innate immunity of the plant. If we can boost many of those innate defenses, we can protect the plants from the majority of these insect attacks in a way that may be more durable and sustainable than current approaches."
The team also includes Tomas Helikar, Susan J. Rosowski associate professor of biochemistry; Scott Sattler, adjunct associate professor of agronomy and horticulture and research molecular biologist with the USDA's Agricultural Research Service; and Rupesh Kariyat of the University of Texas Rio Grande Valley.
The team is focused on one of the most plentiful components found in plants: lignin. It has a central role in forming rigid, stable cell walls and facilitating water transport. Because the polymer is found throughout sorghum -- including on its outer surfaces -- it's one of the first components that sugarcane aphids confront when they insert their needle-like mouthpart into the plant.
But little is known about how, exactly, lignin may help sorghum fend off sugarcane aphids. Louis and Sattler became intrigued by lignin's potential defensive role when they noticed that in some sorghum plants, altered lignin levels impacted the behavior of aphids, and the plant became either more resistant or more susceptible to the pest.
Preliminary data from these plants indicated that the monolignol pathway, which plays a key role in synthesizing lignin, and a gene known as Brown midrib12, or Bmr12, located in the lignin biosynthesis pathway, might be particularly important in driving these changes.
To pinpoint exactly how Bmr12 influences a plant's natural immunity, Louis' team will weave together a variety of approaches -- transcriptomic, biochemical, electrophysiological, histological and computational biology. This wide-ranging, transdisciplinary approach is a major strength of the research.
"This is a holistic approach in understanding plant-aphid interactions, using multiple approaches to answer the question of how Bmr12 is involved in modulating sorghum defenses against aphids," Louis said. "That's how it stands out as a unique project."
The computational component is particularly innovative. Helikar, an expert in computational systems biology, will develop a network analysis model showing how Bmr12's behavior has ripple effects throughout the plant. The system will enable the team to easily test hypotheses about how a change in Bmr12-associated pathways may impact a plant's properties and defense mechanisms.
Louis and Helikar will introduce Husker students, undergraduate and graduate, to these computational approaches through new laboratory modules they're developing as part of the project. The new curriculum pieces are aimed at opening students' eyes to the power of interdisciplinary methods and computational modeling to solve problems in biology, entomology and ecology.
Kariyat, the collaborator at the University of Texas Rio Grande Valley, is leading an additional student outreach effort at a middle school in the Rio Grande Valley, at which more than 90% of students are Hispanic. He will engage these students in inquiry-based experiments focused on plant-insect interactions.
Beyond its role in lignin production, Bmr12 may also influence a plant's indirect defenses by producing volatile organic compounds that strengthen a plant's immunity. When certain pests attack, crops respond by producing these compounds. They strengthen plant tissues against pest-induced damage and send airborne signals to neighboring plants, triggering their defense systems. Louis' team will investigate how disturbing Bmr12-associated pathways could strengthen this protective mechanism.
Long term, Louis envisions the work on Bmr12 as just one piece of the larger puzzle of bolstering plants' natural immunity -- there are many other genes and pathways that researchers can exploit to boost resistance to pests. He doesn't expect that natural immunity methods will completely supplant pesticides but believes their use can be reduced to much lower levels.
"Ultimately, we hope to bring in another tool for farmers that will help them cut down on the use of toxic insecticides," he said.
The research is funded by the Plant Biotic Interactions Program, a joint initiative of the USDA's National Institute of Food and Agriculture and the National Science Foundation.
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