title: Evolutionary mechanisms driving the evolution of a large polydnavirus gene family coding for protein tyrosine phosphatases.
abstract: BACKGROUND
  Gene duplications have been proposed to be the main mechanism involved in genome evolution and in acquisition of new functions. Polydnaviruses (PDVs), symbiotic viruses associated with parasitoid wasps, are ideal model systems to study mechanisms of gene duplications given that PDV genomes consist of virulence genes organized into multigene families. In these systems the viral genome is integrated in a wasp chromosome as a provirus and virus particles containing circular double-stranded DNA are injected into the parasitoids' hosts and are essential for parasitism success. The viral virulence factors, organized in gene families, are required collectively to induce host immune suppression and developmental arrest. The gene family which encodes protein tyrosine phosphatases (PTPs) has undergone spectacular expansion in several PDV genomes with up to 42 genes.
  
  
  RESULTS
  Here, we present strong indications that PTP gene family expansion occurred via classical mechanisms: by duplication of large segments of the chromosomally integrated form of the virus sequences (segmental duplication), by tandem duplications within this form and by dispersed duplications. We also propose a novel duplication mechanism specific to PDVs that involves viral circle reintegration into the wasp genome. The PTP copies produced were shown to undergo conservative evolution along with episodes of adaptive evolution. In particular recently produced copies have undergone positive selection in sites most likely involved in defining substrate selectivity.
  
  
  CONCLUSIONS
  The results provide evidence about the dynamic nature of polydnavirus proviral genomes. Classical and PDV-specific duplication mechanisms have been involved in the production of new gene copies. Selection pressures associated with antagonistic interactions with parasitized hosts have shaped these genes used to manipulate lepidopteran physiology with evidence for positive selection involved in adaptation to host targets.
authors.affiliation: Institut de Recherche sur la Biologie de l'Insecte, UMR CNRS 7261, Faculté des Sciences et Techniques, Université F. Rabelais, Parc de Grandmont, 37200, Tours, France.
authors.forename: Céline
authors.initials: C
authors.lastname: Serbielle
authors.forename: Stéphane
authors.initials: S
authors.lastname: Dupas
authors.forename: Elfie
authors.initials: E
authors.lastname: Perdereau
authors.forename: François
authors.initials: F
authors.lastname: Héricourt
authors.forename: Catherine
authors.initials: C
authors.lastname: Dupuy
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Huguet
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Drezen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019143:Evolution, Molecular; D020440:Gene Duplication; D008969:Molecular Sequence Data; D010802:Phylogeny; D018071:Polydnaviridae / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases / Q000737:chemistry / Q000235:genetics*; D016415:Sequence Alignment; D014863:Wasps / Q000821:virology
chemical_list: D017027:Protein Tyrosine Phosphatases