Activation of plant toxins by herbivorous insects
Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
Final Report Abstract
Plants produce bioactive substances to fight off plant-feeding insects. To avoid that these compounds damage their own tissue, plants often attach sugars to the bioactive substances, which inactivates the bioactive substances. When an insect feeds on the plant, the plant removes the stabilizing sugar, which activates the compounds and makes them toxic or deterrent. While often the plants remove the sugars themselves, sometimes the sugars are removed by the insects. At the moment, it is unclear what consequences this has for the insect, especially whether this changes insect behavior. Dandelions, Taraxacum officinale, produce high amounts of a sugar-containing defense compound in their roots, called taraxinic acid β-D-glucopyranosyl ester, or TA-G for short. TA-G deters the feeding of the larvae of the Maybug (Melolontha melolontha) – a pest also known as the common cockchafer. When Maybug larvae do eat TA-G, the compound is found in their guts but without the sugar. However, it is unclear whether it is the plant or the larva that removes the sugar, and whether the sugar removal affects the behavior of the Maybug larvae. Using chemical analysis and genetic modifications, we investigated what happens when Maybug larvae eat TA-G. We found that the acidity levels in the larvae’s gut inhibits the proteins from the dandelion that would normally cleave the sugar from TA-G. However, the larvae remove the sugar from this defense compound themselves. The protein that does this is an enzyme that is usually involved in the break-down of nutritional carbohydrates: a beta-glucosidase, an enzyme that cuts off sugars. Removing the sugar from TA-G had two seemingly contrasting effects: on the one hand, removing the sugar made larvae growing faster. On the other hand, removing the sugar made the compound foul-tasting, and thereby made the larvae searching for a different food source. Many organism that eats plants, including humans, must deal with substances like TA-G that are stored in an inactive form and are activated either by digestive proteins or specific conditions in the environment. This principle may help to design drugs that are activate only in certain species or organs, or under certain environmental conditions. The insights gained from this project may aid the development of new methods of pest control, or stimulate new ways in medicine to make drugs more specific to the target site.
Publications
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A beta-glucosidase of an insect herbivore determines both toxicity and deterrence of a dandelion defense metabolite. eLife, 10.
Huber, Meret; Roder, Thomas; Irmisch, Sandra; Riedel, Alexander; Gablenz, Saskia; Fricke, Julia; Rahfeld, Peter; Reichelt, Michael; Paetz, Christian; Liechti, Nicole; Hu, Lingfei; Bont, Zoe; Meng, Ye; Huang, Wei; Robert, Christelle AM; Gershenzon, Jonathan & Erb, Matthias
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Natural rubber reduces herbivory and alters the microbiome below ground. New Phytologist, 239(4), 1475-1489.
Böttner, Laura; Malacrinò, Antonino; Schulze, Gronover Christian; van Deenen, Nicole; Müller, Boje; Xu, Shuqing; Gershenzon, Jonathan; Prüfer, Dirk & Huber, Meret
