title: Back to the sea twice: identifying candidate plant genes for molecular evolution to marine life.
abstract: BACKGROUND
  Seagrasses are a polyphyletic group of monocotyledonous angiosperms that have adapted to a completely submerged lifestyle in marine waters. Here, we exploit two collections of expressed sequence tags (ESTs) of two wide-spread and ecologically important seagrass species, the Mediterranean seagrass Posidonia oceanica (L.) Delile and the eelgrass Zostera marina L., which have independently evolved from aquatic ancestors. This replicated, yet independent evolutionary history facilitates the identification of traits that may have evolved in parallel and are possible instrumental candidates for adaptation to a marine habitat.
  
  
  RESULTS
  In our study, we provide the first quantitative perspective on molecular adaptations in two seagrass species. By constructing orthologous gene clusters shared between two seagrasses (Z. marina and P. oceanica) and eight distantly related terrestrial angiosperm species, 51 genes could be identified with detection of positive selection along the seagrass branches of the phylogenetic tree. Characterization of these positively selected genes using KEGG pathways and the Gene Ontology uncovered that these genes are mostly involved in translation, metabolism, and photosynthesis.
  
  
  CONCLUSIONS
  These results provide first insights into which seagrass genes have diverged from their terrestrial counterparts via an initial aquatic stage characteristic of the order and to the derived fully-marine stage characteristic of seagrasses. We discuss how adaptive changes in these processes may have contributed to the evolution towards an aquatic and marine existence.
authors.affiliation: Evolutionary Bioinformatics, Institute for Evolution and Biodiversity, University of Muenster, Huefferstrasse 1, D48149 Muenster, Germany.
authors.forename: Lothar
authors.initials: L
authors.lastname: Wissler
authors.forename: Francisco M
authors.initials: FM
authors.lastname: Codoñer
authors.forename: Jenny
authors.initials: J
authors.lastname: Gu
authors.forename: Thorsten B H
authors.initials: TB
authors.lastname: Reusch
authors.forename: Jeanine L
authors.initials: JL
authors.lastname: Olsen
authors.forename: Gabriele
authors.initials: G
authors.lastname: Procaccini
authors.forename: Erich
authors.initials: E
authors.lastname: Bornberg-Bauer
mesh_terms: D035961:Alismatales / Q000145:classification / Q000235:genetics*; D059001:Aquatic Organisms / Q000145:classification / Q000235:genetics*; D019143:Evolution, Molecular; D008386:Marine Biology; D008969:Molecular Sequence Data; D009792:Oceans and Seas; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics*
chemical_list: D010940:Plant Proteins