PRESS RELEASE
THE APHID GENOME SEQUENCE PROVIDES NEW CLUES ABOUT THE EVOLUTION AND CAN HELP IN THE CROP PESTS MANAGEMENTResearchers from the Centre for Genomic Regulation (CRG) have taken part in the pea aphid genome sequence (Acyrthosiphon pisum).The research, published on the 23th of February at the journal PLoS Biology, presents the complete analyse of this insect’s genome, and starts to disclose the genetic basis that could explain the complex ecology of this parasite.A new vision to understand the general evolution will be given by the aphid genome sequence project. At the same time, it will give many clues about the insects evolution and the relation o co-evolution they set with the symbiotic bacteria they live with.The aphid is one of the most extensive pest in the crop fields. World total damages caused by this insect are estimated in hundreds of million dollars. The aphid is also an insect very used as a model in the researches about interactions between plants and insects, symbiosis, development, phenotypic plasticity...About the aphid
This little insect only feeds on plants. Thanks to its specialized jaw, it sucks the plant sap, which is rich in sugar. This causes direct damages on the plant because it becomes weak. In addition, the insect usually works as a vector of virus that will infect the plant.Because of the sap specific composition, the aphid needs the symbiotic bacterium (Buchnera aphidicola) help which will provide him essential amino acids that can be found in the plant. So, the aphid has co-evolved with this symbiotic bacterium. Some aphid species establish other mutualism relations with various bacteria which provide them ecologic benefits as warm natured or parasitoid resistance.The aphid can reproduce sexual and asexually. These insects have evolved to obtain various vital life circles, in this way, the organisms themselves can develop individuals with phenotypes or very different aspects according to the environmental conditions. For example, they can develop females with or without wings according to the existing dispersion needs when they reproduce themselves.About the aphid genome research
The research of the aphid genome sequence has been carried to term by an international consortium, the “Aphid Genomics Consortium”, leaded by the Human Genome Sequencing Center at the Baylor College of Medicine and composed by more than 20 research groups. Among these groups, there are two of the CRG research groups: the Bioinformatics and Genomics group headed by Roderic Guigó, and the Comparative Genomics group headed by Toni Gabaldón. In Spain, the University of Barcelona, the University of Valencia and the Cavanilles Institute for Biodiversity and Evolution have also participated in this study.The work shows some discoveries that could be related to the unusual characteristics presented by this organism such as: its condition of plan parasite, its ability to reproduce sexual and asexually, and the fact that it has mandatorily co-evolved with its bacterial symbiont. The contributions of the CRG groups have been very important for the work. They have done the comparative analyse of the aphid genome with other species. The researchers compared the sequenced genome with many insect species and other organisms and they could get to some very interesting conclusions. “When comparing the aphid genome with other insects genome we have realized the aphid genome has expanded with duplications more than 2000 families of genes (nearly the 30% of the genome). This implies a genome expansion record amongst insects”, says Toni Gabaldón, the CRG Comparative Genomics group leader. “The expansion of some gene families in the aphid genome has allowed aphids to diversify their functions in order to better adapt to their specific needs, such as being able to live on a diet exclusively based on vegetal sap or regulating their life cycle according to the yearly different seasons, declares Gabaldón.It is believed that all these duplications could have already appeared in the origin of these species. And it seems that the duplicated gens would be involved in the chromatin modification, the miARN synthesis and the sugar transport. It is also believed that some of the aphid development patrons and its great phenotypic plasticity shall be identified by the duplication of the gens related to the development.Because of the fact it is the first sequenced genome of an organism with a forced symbiont that has co-evolved with him, the work reveals that the host and symbiont genomes are coordinated regarding the involved gens in the metabolism. At the same time, it has been seen that the aphid has lost some important genes for the immune system. Even though this can seem strange, that would be explained as a consequence of the co-evolution with its bacterial symbionts, since a strong immune system would make the relation symbiont-host difficult rejecting or eliminating the symbiotic bacterium.The aphid genome presents some bacterial originally genes. A part of these genes could play a role in the symbiosis regulation with Buchnera.So, the analyse of the aphid genome contributes with some clues to the ecology of these animals, and it is expected it will give new points of view for the understanding of the evolved mechanisms, and it could be used to improve the development in the prevention tools for the pest field treatment.Reference work: The International Aphid Genomics Consortium. “Genome Sequence of the Pea Aphid Acyrthosiphon pisum” PLoS Biology (2010). doi: 10.1371/journal.pbio.1000313.  

For further information: Laia Cendrós, Communication & PPRR Dept. Centre for Genomic Regulation (CRG), Dr. Aiguader, 88 – Edif. PRBB, 08003 Barcelona. Tel. +34 93 316 02 37.