title: Phylogenetic analysis of LSU and SSU rDNA group I introns of lichen photobionts associated with the generaXanthoriaandXanthomendoza(Teloschistaceae, lichenized Ascomycetes).
abstract: We studied group I introns in sterile cultures of selected groups of lichen photobionts, focusing onTrebouxiaspecies associated withXanthorias. lat. (includingXanthomendozaspp.; lichen-forming ascomycetes). Group I introns were found inserted after position 798 (Escherichia colinumbering) in the large subunit (LSU) rRNA in representatives of the green algal generaTrebouxiaandAsterochloris. The 798 intron was found in about 25% ofXanthoriaphotobionts including several reference strains obtained from algal culture collections. An alignment of LSU-encoded rDNA intron sequences revealed high similarity of these sequences allowing their phylogenetic analysis. The 798 group I intron phylogeny was largely congruent with a phylogeny of the Internal Transcribed Spacer Region (ITS), indicating that the insertion of the intron most likely occurred in the common ancestor of the generaTrebouxiaandAsterochloris.The intron was vertically inherited in some taxa, but lost in others. The high sequence similarity of this intron to one found inChlorella angustoellipsoideasuggests that the 798 intron was either present in the common ancestor of Trebouxiophyceae, or that its present distribution results from more recent horizontal transfers, followed by vertical inheritance and loss. Analysis of another group I intron shared by these photobionts at small subunit (SSU) position 1512 supports the hypothesis of repeated lateral transfers of this intron among some taxa, but loss among others. Our data confirm that the history of group I introns is characterized by repeated horizontal transfers, and suggests that some of these introns have ancient origins within Chlorophyta.
authors.affiliation: Institute of Plant Biology, University of Zurich, Zollikerstrasse 107, 8008 Zurich, Switzerland Department of Radiation Oncology, University of Michigan, 109 Zina Pitcher Place, Ann Arbor, Michigan 48109, United States.
authors.forename: Shyam
authors.initials: S
authors.lastname: Nyati
authors.affiliation: Department of Ecology, Evolution and Natural Resources and Institute of Marine and Coastal Science, Rutgers University, 59 Dudley Road, New Brunswick, New Jersey 08901, USA.
authors.forename: Debashish
authors.initials: D
authors.lastname: Bhattacharya
authors.affiliation: Faculty of Life- and Environmental Sciences, University of Iceland, Sturlugata 7, 101 Reykjavík, Iceland.
authors.forename: Silke
authors.initials: S
authors.lastname: Werth
authors.affiliation: Institute of Plant Biology, University of Zurich, Zollikerstrasse 107, 8008 Zurich, Switzerland.
authors.forename: Rosmarie
authors.initials: R
authors.lastname: Honegger
keywords: LSU 798 group I intron; Lichen; Photobiont; SSU 1512 group I intron; Trebouxia; Trebouxiophyceae; rbcL