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Deciphering the genetics behind maize's odorous cry for help

press release of January 17, 2006

A German-Swiss study involving the National Centre of Competence in Research (NCCR) Plant Survival has revealed the genetic basis of a chemical stress signal emitted by maize after being attacked by herbivorous larvae. This signal is used to attract parasitic wasps that come to the plant's rescue by laying their eggs in the pest larvae. The study appeared this week in the prestigious American journal "Proceedings of the National Academy of Sciences" (PNAS)*.

For several years now, we know that many plants, in response to attacks by insect pests, release volatile substances that attract the enemies of the pests. This was first demonstrated for maize leaves on which caterpillars were feeding. With the support of the NCCR Plant Survival, Ted Turlings' team at the University of Neuchâtel (Switzerland) joined Joerg Degenhardt and his team at the Max Planck Institute for Chemical Ecology in Jena (Germany) to identify a gene in maize producing the specific cocktail of perfumes that attract females of the beneficial wasp Cotesia marginiventris.

To prove that only one gene is sufficient to generate the appropriate signal, the Jena team inserted the gene in Arabidopsis thaliana, a model plant widely used in laboratory research. Result: the model plant emits the same chemical compounds as a wounded maize plant.

To test this signal's attractant capabilities, a device from the University of Neuchâtel was used. The Cotesia wasps were placed in the centre of a six-arm olfactometer, which looks like a glass octopus and is used to measure the attractiveness of odorous signal. At the arms' extremities different odour source combinations can be tested: a plant that emits a signal or not, in the absence of or in the presence of the pest caterpillar.

The experiment revealed that the Cotesia wasps are indeed attracted by the chemical signal, however there's a condition attached. In order for the wasp to react, it must have had the opportunity to associate the bouquet of perfumes with the caterpillar's presence. Without this "learning" experience, wasps showed not preference for a particular plant odour and many remained immobile in the centre of the olfactometer.

This research offers promising prospects for the use of biological control methods in regions where maize is grown, such as in Mexico where caterpillars cause considerable damage to the crops. It may also contribute towards the reduction of pesticide use.

In April of 2005 Ted Turlings' team had already distinguished itself by identifying the volatile substances emitted in the soil when Diabrotica virgifera virgifera larvae attacked maize roots. The purpose of this cry for help is to attract tiny worms (nematodes) in the soil that will infect and kill the pest larvae.

*Original Article:

The products of a single maize sesquiterpene synthase form a volatile defense signal that attracts natural enemies of maize herbivores

Christiane Schnee*, Tobias G. Köllner*, Matthias Held, Ted C. J. Turlings, Jonathan Gershenzon*,
and Jörg Degenhardt*

*Max Planck Institute for Chemical Ecology, Hans-Knöll Strasse 8, Jena D-07745, Germany; and
Laboratory of Evolutionary Entomology, Institute of Zoology, University of Neuchatel,
Emile-Argand 11-CP2, Neuchatel CH-2007, Switzerland

contacts

Dr. Ted Turlings
University of Neuchâtel
Tel. +41 32 718 3158
ted.turlings@unine.ch

Dr. Matthias Held
University of Neuchâtel
Tel. +41 32 718 3008
matthias.held@unine.ch