Aphids are important agricultural pests and also biological models for studies of insect-plant interactions, symbiosis, virus
vectoring, and the developmental causes of extreme phenotypic plasticity. Here we present the 464 Mb draft genome
assembly of the pea aphidAcyrthosiphon pisum. This first published whole genome sequence of a basal hemimetabolous
insect provides an outgroup to the multiple published genomes of holometabolous insects. Pea aphids are host-plant
specialists, they can reproduce both sexually and asexually, and they have coevolved with an obligate bacterial symbiont.
Here we highlight findings from whole genome analysis that may be related to these unusual biological features. These
findings include discovery of extensive gene duplication in more than 2000 gene families as well as loss of evolutionarily
conserved genes. Gene family expansions relative to other published genomes include genes involved in chromatin
modification, miRNA synthesis, and sugar transport. Gene losses include genes central to the IMD immune pathway,
selenoprotein utilization, purine salvage, and the entire urea cycle. The pea aphid genome reveals that only a limited
number of genes have been acquired from bacteria; thus the reduced gene count ofBuchneradoes not reflect gene transfer
to the host genome. The inventory of metabolic genes in the pea aphid genome suggests that there is extensive metabolite
exchange between the aphid andBuchnera, including sharing of amino acid biosynthesis between the aphid and Buchnera.
The pea aphid genome provides a foundation for post-genomic studies of fundamental biological questions and applied
agricultural problems.
Citation:The International Aphid Geno