Beans use an immune receptor to call in airstrikes on caterpillars

For many years, researchers have recognized that plants possess the remarkable ability to emit volatile organic compounds, which serve as airborne signals to attract their natural predators, such as caterpillars. However, the precise mechanism by which a plant converts the physical act of being consumed into a targeted distress signal has remained a mystery. Adam Steinbrenner, a biologist at the University of Washington, stated, "One thing we didn’t know is how the plant detects the caterpillar in the first place." After extensive experiments with common bean plants conducted in both laboratory settings and agricultural fields in Oaxaca, Mexico, Steinbrenner's team has identified a crucial immune receptor that plays a pivotal role in the plant's defense against caterpillar attacks. When a caterpillar feeds on a plant, it introduces its saliva into the damaged tissue, which contains biological markers known as herbivore-associated molecular patterns (HAMPs). Among these is a peptide called inceptin, which includes an 11-amino acid fragment known as In11. Remarkably, both of these molecules are fragments of ATP synthase, a protein found in the plant's chloroplasts. As the caterpillar consumes the leaves, its digestive enzymes break down the plant's cellular machinery, causing fragments like In11 to be regurgitated onto the leaf's surface in minuscule amounts. Over countless generations, common bean plants have evolved a specialized cell surface receptor, known as the inceptin receptor, designed specifically to detect In11. Upon interaction with In11, this receptor triggers a series of signaling pathways within the plant's cells, activating immune responses. Demonstrating that this particular receptor is responsible for initiating signals that summon predators has proven to be a challenging task. "We were excited to do that, but we needed the perfect comparison plants—those lacking the receptor versus ones with the intact receptor," Steinbrenner explained.