Beans use an immune receptor to call in airstrikes on caterpillars

• 01Adam Steinbrenner's team at the University of Washington identified a single immune receptor in common bean plants that orchestrates anti-caterpillar defense systems after years of experimentation in labs and agricultural fields in Oaxaca, Mexico.
• 02When caterpillars feed on plants, their saliva introduces herbivore-associated molecular patterns (HAMPs) into damaged plant tissues, including a peptide called inceptin and an 11-amino acid fragment called In11.
• 03In11 is a fragment of ATP synthase found in plant chloroplasts that is regurgitated onto leaf surfaces at extremely small concentrations after caterpillar gut enzymes break down plant cellular material.
• 04Plants evolved a specialized cell-surface receptor called the inceptin receptor to detect In11 and trigger immune responses.
• 05Researchers screened 89 Mesoamerican bean varieties and found two that failed to produce ethylene gas when exposed to In11, selecting a Honduran strain called W6 13807 that had a naturally occurring 103-base-pair deletion in the gene encoding the inceptin receptor.
• 06Through selective breeding over several years, researchers created genetically similar bean plants that differed only in having either functional or non-functional inceptin receptors.
• 07Caterpillars feeding on mutant beans with inactive inceptin receptors grew at a rate over 70 percent higher over five days compared to caterpillars on plants with functional receptors.
• 08In plants with functional In11 detection, feeding caterpillars triggered rapid up-regulation of 527 genes including anti-herbivore defense genes, while insensitive plants responded only as if mechanically wounded.
• 09Beans lacking functional inceptin receptors were unable to summon predatory wasps.

Researchers at the University of Washington identified a plant immune receptor that detects caterpillar saliva and triggers both direct defenses and the recruitment of predatory insects. By screening bean varieties and using selective breeding to compare plants with and without the functional inceptin receptor, they found that plants unable to detect the caterpillar signal experienced 70 percent faster caterpillar growth and failed to recruit protective wasps.