title: Genome evolution in the primary endosymbiont of whiteflies sheds light on their divergence.
abstract: Whiteflies are important agricultural insect pests, whose evolutionary success is related to a long-term association with a bacterial endosymbiont, Candidatus Portiera aleyrodidarum. To completely characterize this endosymbiont clade, we sequenced the genomes of three new Portiera strains covering the two extant whitefly subfamilies. Using endosymbiont and mitochondrial sequences we estimated the divergence dates in the clade and used these values to understand the molecular evolution of the endosymbiont coding sequences. Portiera genomes were maintained almost completely stable in gene order and gene content during more than 125 Myr of evolution, except in the Bemisia tabaci lineage. The ancestor had already lost the genetic information transfer autonomy but was able to participate in the synthesis of all essential amino acids and carotenoids. The time of divergence of the B. tabaci complex was much more recent than previous estimations. The recent divergence of biotypes B (MEAM1 species) and Q (MED species) suggests that they still could be considered strains of the same species. We have estimated the rates of evolution of Portiera genes, synonymous and nonsynonymous, and have detected significant differences among-lineages, with most Portiera lineages evolving very slowly. Although the nonsynonymous rates were much smaller than the synonymous, the genomic dN/dS ratios were similar, discarding selection as the driver of among-lineage variation. We suggest variation in mutation rate and generation time as the responsible factors. In conclusion, the slow evolutionary rates of Portiera may have contributed to its long-term association with whiteflies, avoiding its replacement by a novel and more efficient endosymbiont.
authors.affiliation: Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de València, Spain.
authors.forename: Diego
authors.initials: D
authors.lastname: Santos-Garcia
authors.affiliation: Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de València, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Vargas-Chavez
authors.affiliation: Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de València, Spain Unidad Mixta de Investigación en Genómica y Salud, FISABIO-Salud Pública and Universitat de València, Spain.
authors.forename: Andrés
authors.initials: A
authors.lastname: Moya
authors.affiliation: Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de València, Spain Unidad Mixta de Investigación en Genómica y Salud, FISABIO-Salud Pública and Universitat de València, Spain.
authors.forename: Amparo
authors.initials: A
authors.lastname: Latorre
authors.affiliation: Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de València, Spain Unidad Mixta de Investigación en Genómica y Salud, FISABIO-Salud Pública and Universitat de València, Spain francisco.silva@uv.es.
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Silva
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D016680:Genome, Bacterial; D023281:Genomics; D044129:Halomonadaceae / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D006430:Hemiptera / Q000145:classification / Q000382:microbiology*; D013559:Symbiosis
keywords: Portiera; amino acid biosynthesis; divergence time; endosymbiont; genome reduction; genome stasis; molecular evolution; whiteflies