The pea aphid genome fully-sequenced.

Two of the groups in our programme (Gabaldón and Guigó) have participated in the analysis of the genomic sequence of the pea aphid Acyrtosiphon pisum, published this week in PLoS Biology. This first published genome of a basal hemimetabolous insect, provides an out-group for comparison with other sequenced insects, and pavesthe way to elucidate molecular mechanisms in this emerging model species.

Pea aphids are host-plant specialists, they can reproduce both sexually and asexually, and they have coevolved with an obligate bacterial symbiont for more than 100 million years. The analysis of its genome has revealed many peculiarities such as large family expansions that affect roughly 30% of the genome (the record among insects). Such expansions have allowed many adaptations in aphids such as the possibility of taking the most of their mononotonous diet (plant sap) by diversifying their families of sugar and amino acid transporters. Other expansions may explain striking aspects of the complex life cycle of aphids, such as their great phenotipic plasticity, regulated by environmental signals (winged vs non-winged females for instance). Besides gene expansions, gene losses have also played a role in shaping this insect genome. Pea aphids lack selenoproteins and many genes of the immune defense system. This softeneed defense system might result from the establishment of the obligate relationship with a bacterial symbiont.  The pea aphid is the first genome in which phylogenetic analyses for every single gene have been incorporated in the genome annotation process, thus allowing accurate functional assignments and detection of gene duplications. All evolutionary histories of aphid genes can be viewed at PhylomeDB.