The sequencing also allows scientists studying the spread of agricultural diseases to further understand the relationship between a virus, the host insect and the plant. Aphids are also major vectors of viral plant disease, which cause severe economic damage for agriculture. Some viruses have evolved to facilitate their transmission by aphids and the newly published genome sequence will allow scientists to understand the physiological, genetic and molecular basis of this critical interaction. Aphids feed on plant juices which they obtain from the phloem tissue of leaves and stems using long piercing mouthparts. Phloem is rich in carbohydrates, but low in the nitrogenous compounds which complex organisms need to make proteins to survive. Aphids have a highly developed gut and the genome sequence reveals many genes for sugar transporter proteins but oddly are missing common genes involved in making some amino acids. Remarkably, symbiotic bacteria living inside the aphid provide these missing proteins.
One of the most curious findings of this sequencing project is the absence of many genes involved in defending the insect from pathogens, parasites and predators. A large part of the typical insect immune system which is well studied in other insects, is absent from the Pea Aphid. This is surprising as Pea Aphids are attacked by a variety of natural enemies ranging from fungal diseases to parasitoid wasps.
"It is likely that aphids are selected for extremely high rates of reproduction, they have to colonise a plant and produce offspring before their enemies find and exterminate them," said Godfrey. "We know there are tradeoffs between defence and other fitness components and in Aphids natural selection may have favoured reproduction over defence."
"Biologists working on the pea aphid now have a valuable new set of tools to attack novel questions," concludes Godfrey. "Studies on the pea aphid will
|Contact: Ben Norman|