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Chemical war: How plants starve bugs

MICHIGAN STATE (US) — In the ongoing battle between plants and the pests that love to eat them, a few plants respond with lethal force, producing an enzyme that starves attackers.

Understanding the chemical weaponry of this war could lead to novel approaches to protect crops, a new study suggests.

All plants produce the enzyme threonine deaminase, or TD1. Gregg Howe, a professor of biochemistry and molecular biology at Michigan State University, focused on potato and tomato plants, which also have the ability to produce a closely related enzyme TD2 when attacked by caterpillars.

Rather than repel caterpillars, however, TD2’s devastating effects come later—in the pests’ stomachs. TD2 goes to work in the gut of caterpillars to degrade threonine, a key nutrient they need to grow. In essence, the plant actively starves the caterpillar.

The battle sees plants continually developing chemical defenses to fend off their herbivore adversaries’ ever-adapting arsenal, says Howe, who is coauthor of the study reported in the current issue of the Proceedings of the National Academy of Sciences.

“The arms-race paradigm is quite important for explaining plant chemical diversity and interactions between plants and herbivores in general,” he says. “Unfortunately, our understanding of the molecular evolution of chemical defensive traits is still in its infancy.”

The ability of TD2 to break down threonine is activated only after it enters the insect’s gut in the form of a chewed up leaf. The capacity of TD2 as a defense against pests was bolstered when the research team identified the enzyme’s x-ray crystal structure.

Seeing that it had a more stable structure and is more resilient than TD1 or other TDs, suggests that the enzyme is a key that could lead to new forms of pesticides, Howe says.

“This confirms a role for gene duplication in the evolution of plant defenses that target the digestive process of insects,” he adds. “It represents a novel approach to protecting plants against pests.”

The study is a collaboration between the MSU-Department of Energy Plant Research Laboratory and the University of Wisconsin-Madison. The research was funded by the U.S. Department of Agriculture and the U.S. Department of Energy and supported by MSU AgBioResearch.


“The arms-race paradigm is quite important for explaining plant chemical diversity and interactions between plants and herbivores in general,” says Gregg Howe, a professor of biochemistry and molecular biology. “Unfortunately, our understanding of the molecular evolution of chemical defensive traits is still in its infancy.” (Credit: Kurt Stepnitz)

More news from Michigan State University: http://news.msu.edu/

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