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Aphid genome reveals its 'Achilles heel'
The genome of the aphids is revealing secrets that may lead to the development of plants that can fight back against the troublesome pest, say researchers.

Dr Owain Edwards of CSIRO Entomology in Perth and colleagues report their genome sequence of the Pea Aphid (Acrythosiphon pisum) in the current issue of PLOS Biology .

"What we're looking for is some sort of an Achilles heel that we might be able to affect in some way to be able to control aphids efficiently without using ... conventional insecticides," says Edwards.

Edwards says the major problem with sap-sucking aphids is that they spread viruses between plants.

They reproduce incredibly fast and are very clever at adapting to their environment.

For example, when it is warm, they reproduce asexually, with females giving live birth to clones of themselves.

In cold countries as winter approaches aphids switch from asexual to sexual reproduction within just two generations.

This ensures production of eggs, which can survive freezing temperatures better than live young.

Aphids can also transform in one generation from being unwinged to winged if they need to escape an ailing or overcrowded plant host, says Edwards.
Mystery of adaptation

Genetic recombination during sexual reproduction usually provides the genetic diversity necessary for adaptation to the environment.

But in relatively warm countries like Australia, aphids mainly reproduce asexually but are very clever at adapting to their environment.

Edwards says research on the aphid genome suggests the explanation for aphid's "environmental memory", lies in epigenetics.

In a companion paper in the March issue of Insect Molecular Biology, Edwards and colleagues report evidence of DNA methylation of certain genes that regulate aphid development.

They found methylation of these genes differed in winged versus unwinged aphids, as well as sexual versus asexual aphids, with the same genome.

This provides evidence methylation plays an important role in aphid adaptation, says Edwards.
Pest controlling plants?

Edwards says the findings give scientists researching pest control options to explore.

Rather than killing aphids with pesticides, and pressuring them to evolve resistance, he says scientists could instead try todisrupt the normal growth of aphids using the new genetic knowledge.

"For example, if we were able to come up with a way of being able to disrupt their ability to produce wings then they would have difficulty moving from one plant to another," says Edwards.

Edwards says one idea is to develop a transgenic plant that contains a DNA sequence designed to disrupt epigenetic modifications in aphids.

For example, the DNA sequence could be designed to bind to, and silence, the aphid genes that regulate methylation.

The DNA would be transferred to the aphid as RNA when it sucks the sap of the plant.

Edwards is currently trialling this approach in test crops related to canola and legumes with an international research consortium.

He says another option would be to inhibit the proteins involved in methylation.

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