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Systematics Section / ASPT

Quandt, Dietmar [2], Müller, Kai [3], Stech, Michael [4], Hilu, Khidir W. [1], Borsch, Thomas [3].

Molecular evolution of the chloroplast trnL-F region in land plants.

The trnL group I intron and the spacer between trnL and trnF are one of the most widely utilized non-coding regions in plant systematics. Comparing the trnL-trnF region in land plants with algal cp genomes reveals an arrangement and localization that is unique to land plants. In algal chloroplast genomes both tRNA genes are widely scattered. Secondary structure analyses show high sequence variability to be confined to certain stem-loop regions (P6, P8), whereas P, Q, R, S elements of the group I intron catalytic core are highly conserved across land plants. Considerable length differences, particularly in P8 and the spacers, were observed between the various land plant lineages, with sequences of mosses and liverworts generally being shorter than those of other lineages. It appears that certain elements in the trnL-F intergenic spacer and in the most variable P8 stem-loop region of the trnL intron have originated by independent nucleotide additions. These elements do not share a common evolutionary history across all land plant lineages below seed plants because repeated sequence parts have further diversified and actually represent internal paralogous stretches. It further appears that most of the length variation in the trnL-F spacer occurs between the putative sigma70-type bacterial promoter motif upstream of trnF and the trnL 3´exon. Apart from leptosporangiate ferns and lycophytes, this conserved promoter motif is present in most land plant lineages sampled, as well as in Chaetosphaeridium. Based on the structural data it is further shown that compensating base pair changes (CBC) in helical elements of the intron significantly contribute to the phylogenetic structure. However, the contribution of CBCs to the total amount of phylogentic signal is found to be less significant within terminal land plant lineages.

1 - Virginia Polytechnic Institute and State University, Department of Biology, Blacksburg, Virginia, 24061, USA
2 - Technische Universität Dresden, Botanisches Institut, Zellescher Weg 22, Dresden, D-01062, Germany
3 - Rheinische Friedrich-Wilhelms-Universität Bonn, Nees-Institut für Biodiversität der Pflanzen, Meckenheimer Allee 170, Bonn, D-53115, Germany
4 - Freie Universität Berlin, Institut für Biologie, - Systematische Botanik und Pflanzengeographie, Altensteinstraße 6, Berlin, D-14195, Germany

group I intron
land plants
molecular evolution

Presentation Type: Paper
Session: 58-12
Location: Cottonwood B (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 4:30 PM
Abstract ID:287

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