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Comparative Chloroplast Genomics

Palmer, Jeffrey D. [1], Rice, Danny W. [1].

Rate Heterogeneity and Horizontal Gene Transfer in Chloroplast Genome Evolution.

Several studies have reported relatively modest, lineage-specific variation in rates of chloroplast synonymous substitutions (across most or all genes) or nonsynonymous substitutions (in a particular gene). We will report several cases of dramatic elevation in rates of nonsynonymous substitutions. These involve clpP, ycf4, and the RNA polymerase genes and occur in disparate lineages of angiosperms. In certain of these cases, there is clear evidence for positive selection operating on the evolution of the proteins encoded by these gene. Several recent studies have shown that plant mitochondrial genes are subject to widespread and evolutionarily frequent horizontal transfer during land plant evolution. In contrast, there is no published evidence for horizontal transfer of chloroplast genes in land plants, despite roughly 100-fold greater sequencing of this genome. We conducted a systematic, gene-by-gene phylogenetic analysis of all sequenced chloroplast genomes and found only one well-supported case of horizontal gene trasfer in land plants. Interestingly, this transfer has led to a highly chimeric gene, consisting of a mosaic of vertically and horizontally transmitted segments.


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1 - Indiana University, Department of Biology, Jordan Hall, 1001 East Third Street, Bloomington, Indiana, 47405, USA

Keywords:
Chloroplast genome
horizontal gene transfer
substitution rates
positive selection.

Presentation Type: Symposium or Colloquium Presentation
Session: 2-3
Location: Salon K - Austin Grand Ballroom/Hilton
Date: Monday, August 15th, 2005
Time: 9:15 AM
Abstract ID:86


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