The gene's role in creating resistance to Hessian flies was a surprise to U.S. Department of Agriculture and Purdue University researchers, discoverers of the gene and its function. They made the finding as they investigated new, long-term methods to protect wheat from insect damage.
"This is a different kind of defense than we were expecting," said Christie Williams, a USDA-Agricultural Research Service scientist and Purdue Department of Entomology adjunct assistant professor. "Usually we expect the plant to fortify its cell walls or make poisons to use against insects and pathogens."
Instead, the researchers found that a specific protein, called HFR-3, one of a group of substances called lectins, is capable of binding with a carbohydrate complex in the Hessian fly larvae. The lectin acts as a key to the carbohydrate structure, known as a chitin.
When the larvae attack a resistant plant, the plant's lectin production quickly increases by as much as 3,000 times. The larvae then ingest the lectin. This interaction probably damages the larvae's chitin-rich mid-gut lining so that it can't absorb nutrients from the plant, causing the insects starve, Williams said.
Some Hessian fly larvae, which are called virulent, are capable of ridding their bodies of lectin and surviving. Avirulent larvae are unable to deactivate the lectin.
However, the researchers believe that plants resistant to Hessian fly invasions may make several strains of lectins in response to virulent larvae, Williams said.
Results of the study are published in the January issue of the journal Molecular Plant Pathology.
Researchers also discovered that not only do lectins damage the insect's mid-stomach, the lectins also taste bad and have some toxicity.