26 February 2010
Secrets of the pea aphid unveiled
Aphids are serious agricultural pests, not only because they consume plant saps, but also because they transmit plant diseases that destroy all kind of crop plants. A large international research consortium with the participation of a research group around Professor Cornelis Grimmelikhuijzen at the University of Copenhagen has now sequenced the genome from the pea aphid Acyrthosiphum pisum. This work, which was published in the high impact factor journal PLoS Biology this week, will enable researchers to better understand molecular processes occurring in aphids. This improved understanding of aphids will eventually lead to the prevention of aphid attacks on crop plants and the transmission of aphid-born plant diseases.
Facts about the project
- The project has been carried out by an international research consortium (The International Aphid Genome Consortium), consisting of 300 researchers from 82 laboratories in 15 countries.
- The sequencing and assembly of the genome has been performed in USA (project coordinator, Professor Stephen Richards from the Human Genome Sequencing Center, Baylor College of Medicine, Houston, USA), whereas the other groups have helped with the interpretation of the genome.
- The pea aphid's genome consists of 520 million nucleotides (genome building blocks) of which 460 million have been sequenced in the project. The genome contains about 34,600 genes, which code for 34,600 proteins, which is twice as much as that found in the fruitfly Drosophila melanogaster.
- The sequence of the aphid genome is the blue print for a better understanding of the molecular process occurring in aphids. Previously, the aphid was only regarded as a "black box", where researchers did not know so much of what was going on inside the animal. Aphids suck up plant sap, which contains a high concentration of sugar (sucrose). After sequencing its genome, we can now see that the aphid has a large number (34) of proteins facilitating sugar transport from the gut to the blood circulation.
Facts about aphids
- Many aphids feed on agricultural plants and cause worldwide crop losses of hundreds of million dollars annually. This crop damage is not so much caused by the feeding itself (sap loss), but mainly because aphids transmit pathogenic plant viruses that subsequently destroy the food plants.
- Aphids have interesting life cycles, including females that lay fertilized eggs and females that give birth to live offspring from eggs that are not fertilized and which are "clones" from the mother (a process called parthenogenesis). These parthenogenic embryos develop within their mothers and sometimes embryos develop inside embryos, such that mothers carry their daughters and granddaughters within them ("Babushka dolls"). This way of reproduction promotes short generation times, allowing aphid colonies to grow rapidly on a newly infected plant.
- Aphids live from plant sap, which consists of water and a high concentration of sugars, but otherwise of not much else. Aphids need essential amino acids for their protein biosynthesis. For this, they host special bacteria (Buchnera aphidicola) that they keep in specialized cells called bacteriocytes. The bacteria get sugars from their hosts and produce, in exchange, amino acids that are used by the aphid for building up their proteins. Such a process, where two partners take advantage of each other, is called symbiosis. Although the sequencing project was designed to target the genome of the pea aphid, also the genome of the symbiotic bacterium was sequenced in the same process. These results for the bacterium genome gave interesting information about the symbiotic interactions between the pea aphid and its bacterial partner.
The International Aphid Genomics Consortium (2010). Genome Sequence of the Pea Aphid Acyrthosiphon pisum. PLoS Biology 8(2): e1000313.