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Systematics Section / ASPT

Won, Hyosig [1], Renner, Susanne [2].

The evolution of the trnT-trnF region in the gymnosperm lineage Gnetales.

We have analyzed the evolution of the plastid trnT-trnF region in the gnetalean genera Gnetum, Welwitschia, and Ephedra, with especially dense sampling in Gnetum for which we included 41 accessions repesenting 25 species. The region consists of the trnL intron, a group I intron, and the trnT-trnL and trnL-trnF intergenic spacers. The intron has a conserved secondary structure and contains elements that are homologous over a wide taxonomic spectrum from eubacteria to chloroplast, while the spacers are so variable in length and composition that homology cannot be found even within Gnetales. Palindromic sequences that form hairpin structures were detected in the trnL-trnF spacer region of Gnetum, but neither spacer contained conserved promoter elements for the tRNA genes. The high sequence variation in the two spacers, absence of promoter elements, and presence of hairpin structures, together with the function of enzymes involved in tRNA expression and processing, lead us to propose that tRNA transcription in Gnetales can proceed with only internal promoter elements, and does not involve promoters in the spacer regions. The seeming neutrality of trnT-trnF spacer evolution would then be attributable to the spacersí escape from functional constraints. Our poster also proposes a model for the expression and processing of the trnT-trnF region.


1 - Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, Pennsylvania, 15213, U.S.A.
2 - University of Missouri-St. Louis, Biology, 8001 Natural Bridge Road, St. Louis, Missouri, 631321, USA

Keywords:
Gnetum
Gnetales
trnL intron
trnT-trnL IGS
trnL-trnF IGS
molecular evolution.

Presentation Type: Poster
Session: 32-126
Location: Special Event Center (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 12:30 PM
Abstract ID:587


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