Comparative gene mapping as a tool to understand the evolution of pest crop insect chromosomes

The extent of conservation of synteny and gene order in aphids has been previously investigated only by comparing a small subset of linkage groups between the pea aphid Acyrthosiphon pisum and few other aphid species. Here we compared the localization of eight A. pisum scaffolds (covering 5,3 Mb and 83 genes) in respect to the fly Drosophila melanogaster Muller elements identifying orthologous loci spanning all the four A. pisum chromosomes (as evidenced by FISH experiments). Comparison of the genetic maps revealed that the gene order is not conserved, but a macroscale synteny is present across different loci suggesting that the study of the fly Muller elements could favour the identification of chromosomal markers useful for the study of chromosomal rearrangements in aphids. The presence of chromosomal portions with homology between aphids and Diptera is particularly relevant in view of the holocentric nature of the aphid chromosomes, suggesting that, although holocentrism could favour local rearrangement, the overall gene content of the chromosomes is not altered. A. pisum is the first aphid species to have its genome sequenced and it has been suggested a substantial synteny of gene order and orientation with other Aphidinae so that the finding of several chromosomal regions in synteny between Diptera and Hemiptera indicates that the genomic tools developed in A. pisum will be broadly useful also for the study of other aphid species of relevant agricultural interest.