www.checkbiotech.org ; www.raupp.info ; www.czu.cz

Max Planck researchers in Jena, Germany have identified a gene which
produces a chemical 'cry for help' that attracts beneficial insects to
damaged plants, January 2006.

Corn plants emit a cocktail of scents when they are attacked by certain
pests, such as a caterpillar known as the Egyptian cotton leaf worm.
Parasitic wasps use these plant scents to localize the caterpillar and
deposit their eggs on it, so that their offspring can feed on the
caterpillar. Soon after, the caterpillar dies and the plant is relieved from
its attacker.

In the case of corn, only one gene, TPS10, has to be activated to attract
the parasitic wasps. This gene carries information for a terpene synthase,
an enzyme forming the sesquiterpene scent compounds that are released by the
plant and attract wasps toward the damaged corn plant. Since this mechanism
is based only on a single gene, it might be useful for the development of
crop plants with a better resistance to pests (PNAS, Early Edition, January
16-20, 2006).

At least 15 species of plants are known to release scents after insect
damage, thus attracting the enemies of their enemies. Scientists term this
mechanism "indirect defence". A previous cooperation by the scientists in
Neuchatel and Jena showed that indirect defence functions not only above
ground, but also below the earth's surface [1].

To understand the biochemistry behind this plant defence, biologists of the
Max Planck institute studied corn plants, caterpillars of the species
Spodoptera littoralis (Egyptian cotton leaf worm) and parasitic wasps of the
species Cotesia marginiventris. Deciphering the complex mix of scents that
the plants release after damage offered clues as to which classes of enzymes
might be important for scent production.

The researchers isolated various genes encoding terpene synthases, the
enzymes that produce these scents. One of these genes, TPS10, produced the
exact bouquet of nine scent compounds that was released by the damaged corn
plant.

To demonstrate that TPS10 is indeed the important gene, the scientists
introduced TPS10 into another plant, called Arabidopsis thaliana, which then
released the same scents that have been observed in corn. To test whether
these scents do attract the parasitic wasps, these plants were tested in an
olfactometer, a device to study insect behaviour.

The researchers placed scent-producing as well as unmodified plants in the
six arms of the olfactometer. When the predatory wasps were set free in the
central cylinder of the olfactometer, they flew towards the scent-producing
plants.

The experiments led to an additional, surprising result: in order to react
this way, the wasps needed a first exposure to both the corn scent and the
caterpillar which led them to associate the two. Young, "naive" wasps
without this experience could not distinguish between scent-producing plants
and control plants, or failed to move at all.

[www.mpg.de]

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