Insect or microbe: plants recognize their attackers and respond by producing specific internal signals that induce the appropriate chemical defenses. That is the main conclusion of a study at the Center for Medical, Agricultural and Veterinary Entomology operated in Gainesville, Florida (USA) by the USDA’s Agricultural Research Service, to which the team around Professor Ted Turlings of the University of Neuchâtel, Switzerland, has contributed. The study was published online on March 18, 2013 in PNAS. When attacked, plants produce cascades of molecular reactions aimed at neutralizing their specific opponents. In response to insect attack plants produce toxins that directly affect the herbivore, but they also emit an odorous cry for help that attracts natural enemies of the pest, thus ensuring indirect protection of the plants. However, the biochemical mechanisms which trigger these defenses have been poorly understood until now. The research to which the biologists of the University of Neuchâtel contributed is directed precisely at this missing link. It has led to the identification of a peptide called ZmPep3, which maize plants produce when their leaves are eaten by herbivorous caterpillars. This peptide triggers the production of insecticidal substances, as well as the emission of a particular odor that specifically attracts natural enemies of the pest, in this case a parasitic wasp that lays its eggs in the caterpillars. To determine the attractiveness of odorous signals, the Gainesville team turned to the Neuchâtel group of experts, known for their discovery of the cry for help in plants.
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