How whiteflies defuse mustard oil bombs

Crucifer plants like arugula and cabbage have spicy flavors thanks to a chemical defense system called the mustard oil bomb. When the plant is damaged, it releases a glucose-capped protoxin and a hydrolase enzyme. The enzyme removes the sugar to form an isothiocyanate that humans find pleasant but that most insects learn to avoid. The whitefly Bemisia tabaci, a sap-sucking pest found worldwide, is a notable exception. A research team led by biochemist Daniel Vassão at the Max Planck Institute for Chemical Ecology has found that rather than avoiding mustard oil bombs, whiteflies defuse them with a sweet trick. The team discovered that whiteflies use carbohydrates in the plant’s own sap to add even more sugars to the protoxin cap via transglucosidase enzymes, which the insects primarily use to dispose of waste (Nat. Chem. Biol. 2020, DOI: 10.1038/s41589-020-00658-6). As a result, the protoxin is no longer recognized by the plant’s hydrolase enzyme and the bomb is preemptively disarmed. Given that whiteflies are not specialized to consume crucifers, Vassão wonders what other chemical defense systems the insects are able to disarm. “There’s so much still to be found in insect chemistry,” he says. “The more we look, probably the more creative biochemistry we’re going to find.”