Beans Recruit Immune Receptors to Attack Caterpillars
▼ Summary
– Plants release volatile organic compounds to attract predators of herbivores, but how they detect being eaten was unknown.
– A team led by Adam Steinbrenner identified a single immune receptor in common bean plants that orchestrates the anti-caterpillar defense response.
– Caterpillar saliva contains herbivore-associated molecular patterns (HAMPs), including inceptin and its fragment In11, which are pieces of the plant’s own proteins.
– When caterpillars feed, their gut enzymes fragment plant proteins, and In11 is regurgitated onto the leaf surface at very low concentrations.
– The inceptin receptor on plant cells detects In11 and triggers a signaling cascade that initiates immune responses, including predator-summoning signals.
For years, researchers have known that plants under attack can release volatile organic compounds,essentially chemical cries for help,to attract predators that eat their attackers, like caterpillars. What remained a mystery was the precise mechanism: how does a plant translate the simple act of being chewed into a targeted, distress signal that summons reinforcements?
“One thing we didn’t know is how the plant detects the caterpillar in the first place,” explains Adam Steinbrenner, a biologist at the University of Washington. After extensive fieldwork and lab experiments with common bean plants in Oaxaca, Mexico, Steinbrenner’s team has now identified a single immune receptor that acts as the master switch for this anti-caterpillar defense system.
The role of caterpillar saliva
When a caterpillar feeds, it deposits its saliva directly into the plant’s wounded tissues. That saliva carries biological markers known as herbivore-associated molecular patterns, or HAMPs. One key HAMP is a peptide called inceptin, along with an 11-amino acid fragment of it named In11. Remarkably, both of these molecules are actually fragments of the plant’s own ATP synthase enzyme, found in chloroplasts. As the caterpillar digests leaf tissue, its gut enzymes break down the plant’s cellular machinery, and pieces like In11 are regurgitated back onto the leaf’s surface,in incredibly tiny amounts.
Over millions of years, plants such as the common bean have evolved a specialized cell-surface receptor, aptly named the inceptin receptor, just to detect In11. When this receptor binds to In11, it triggers a signaling cascade inside the plant’s cells, launching immune responses. However, proving that this specific receptor is the one responsible for releasing the predator-attracting signals proved challenging. “We were excited to do that, but we needed the perfect comparison plants,plants lacking the receptor versus ones that have the intact receptor,” Steinbrenner says.
(Source: Ars Technica)
