title: Evolutionary study of duplications of the miRNA machinery in aphids associated with striking rate acceleration and changes in expression profiles.
abstract: BACKGROUND
  The sequencing of the genome of the pea aphid Acyrthosiphon pisum revealed an unusual expansion of the miRNA machinery, with two argonaute-1, two dicer-1 and four pasha gene copies. In this report, we have undertaken a deeper evolutionary analysis of the phylogenetic timing of these gene duplications and of the associated selective pressures by sequencing the two copies of ago-1 and dcr-1 in different aphid species of the subfamily Aphidinae. We have also carried out an analysis of the expression of both copies of ago-1 and dcr-1 by semi-quantitative PCR in different morphs of the pea aphid life cycle.
  
  
  RESULTS
  The analysis has shown that the duplication of ago-1 occurred in an ancestor of the subfamily Aphidinae while the duplication of dcr-1 appears to be more recent. Besides, it has confirmed a pattern of one conserved copy and one accelerated copy for both genes, and has revealed the action of positive selection on several regions of the fast-evolving ago-1b. On the other hand, the semi-quantitative PCR experiments have revealed a differential expression of these genes between the morphs of the parthenogenetic and the sexual phases of Acyrthosiphon pisum.
  
  
  CONCLUSIONS
  The discovery of these gene duplications in the miRNA machinery of aphids opens new perspectives of research about the regulation of gene expression in these insects. Accelerated evolution, positive selection and differential expression affecting some of the copies of these genes suggests the possibility of a neofunctionalization of these duplicates, which might play a role in the display of the striking phenotypic plasticity of aphids.
authors.affiliation: INRA, UMR 1349 IGEPP, Le Rheu, 35653, France.
authors.forename: Benjamín
authors.initials: B
authors.lastname: Ortiz-Rivas
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Jaubert-Possamai
authors.forename: Sylvie
authors.initials: S
authors.lastname: Tanguy
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Gauthier
authors.forename: Denis
authors.initials: D
authors.lastname: Tagu
authors.forename: Rispe
authors.initials: R
authors.lastname: Claude
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D001042:Aphids / Q000235:genetics*; D060565:Argonaute Proteins / Q000145:classification / Q000235:genetics; D019143:Evolution, Molecular; D005260:Female; D005785:Gene Conversion; D020440:Gene Duplication; D020869:Gene Expression Profiling; D019476:Insect Proteins / Q000145:classification / Q000235:genetics*; D008297:Male; D035683:MicroRNAs / Q000235:genetics*; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D012098:Reproduction / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D043244:Ribonuclease III / Q000145:classification / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D060565:Argonaute Proteins; D019476:Insect Proteins; D035683:MicroRNAs; D043244:Ribonuclease III