Journal of Molecular Evolution

, Volume 64, Issue 3, pp 285–298 | Cite as

Evolution of Pleopsidium (Lichenized Ascomycota) S943 Group I Introns and the Phylogeography of an Intron-Encoded Putative Homing Endonuclease

  • Valérie Reeb
  • Peik Haugen
  • Debashish Bhattacharya
  • François Lutzoni


The sporadic distribution of nuclear group I introns among different fungal lineages can be explained by vertical inheritance of the introns followed by successive losses, or horizontal transfers from one lineage to another through intron homing or reverse splicing. Homing is mediated by an intron-encoded homing endonuclease (HE) and recent studies suggest that the introns and their associated HE gene (HEG) follow a recurrent cyclical model of invasion, degeneration, loss, and reinvasion. The purpose of this study was to compare this model to the evolution of HEGs found in the group I intron at position S943 of the nuclear ribosomal DNA of the lichen-forming fungus Pleopsidium. Forty-eight S943 introns were found in the 64 Pleopsidium samples from a worldwide screen, 22 of which contained a full-length HEG that encodes a putative 256-amino acid HE, and 2 contained HE pseudogenes. The HEGs are divided into two closely related types (as are the introns that encode them) that differ by 22.6% in their nucleotide sequences. The evolution of the Pleopsidium intron-HEG element shows strong evidence for a cyclical model of evolution. The intron was likely acquired twice in the genus and then transmitted via two or three interspecific horizontal transfers. Close geographical proximity plays an important role in intron-HEG horizontal transfer because most of these mobile elements were found in Europe. Once acquired in a lineage, the intron-HEG element was also vertically transmitted, and occasionally degenerated or was lost.


Group I intron mobility Homing endonuclease gene (HEG) Ribosomal RNA Lichen-forming fungus Pleopsidium Phylogeography Ancestral state reconstruction 



We thank Tassilo Feuerer, Ester Gaya, Josef Hafellner, Christine Keller, Jolanta Miadlikowska, Claude Roux, Christophe Scheidegger, Peter Scholz, and Mohammad Sohrabi, as well as the curators of the Herbaria of B, BG, C, CANL, DUKE, GZU, M, O, and TSB, for providing dry material used in this study. We are grateful to Dawn Simon for her help in the laboratory, Claude Roux for identification of specimens, Frank Kauff and Cymon Cox for their help in computer work, Molly McMullen for editing, Mike Skakuj for advice in producing the distribution map, and members of the Lutzoni laboratory as well as two anonymous reviewers for comments on the manuscript. We gratefully acknowledge support from two grants from the National Science Foundation, USA (Doctoral Dissertation Improvement Grant DEB-0105194 to F.L. and V.R. and Grant MCB 01-10252 to D.B.), and a Biology Grant-In-Aid from Duke University, three A. W. Mellon Training Grants from Duke University, two Grants-in-Aid of Research from Sigma-Xi, and a Graduate Fellowship from the Mycological Society of America (all to V.R.).


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Copyright information

© Springer Science+Business Media, Inc. 2007

Authors and Affiliations

  • Valérie Reeb
    • 1
  • Peik Haugen
    • 2
  • Debashish Bhattacharya
    • 3
  • François Lutzoni
    • 1
  1. 1.Department of BiologyDuke UniversityDurhamUSA
  2. 2.Department of Molecular BiotechnologyInstitute of Medical Biology, University of TromsøTromsøNorway
  3. 3.Department of Biological Sciences and Roy J. Carver Center for Comparative GenomicsUniversity of IowaIowa CityUSA

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