Recent Topics Posters
McCoy, Skip K R , Peery, Rhiannon , Kuehl, Jennifer V. , Boore, Jeffrey , Raubeson, Linda A. .
Ephedra and Welwitschia: Divergence and Loss in Two Rapidly Evolving Gnetalean Plastid Genomes.
We have sequenced two gnetalean plastid genomes, from Welwitschia mirabilis and Ephedra viridis. These genomes are normal in that they both show quadripartite structure, with large and small single copy regions separated by two copies of the large rRNA-containing Inverted Repeat. These two plastomes also share numerous unusual characteristics. Both show multiple gene order changes, an unusually high percent of the genome sequence that codes for product, expanded JLA boundaries similar to the 495bp residual IR in Pinus thunbergii, and reduced gene content. Both genomes have lost functional copies of all eleven NADH dehydrogenase genes, as well as the accD, rpl23, and rps16 genes. Welwitschia, but not Ephedra, retains ndhB as a pseudogene. Welwitschia has lost functioning copies of the three chl genes and clpP, which Ephedra retains, although clpP in Ephedra has lost its introns. At the nucleotide level, for 57 shared protein-coding genes, we have compared evolutionary rates by comparing pairwise distances. For each gene, an average pairwise distance for non-gnetalean seed plants was calculated. Then, a pairwise distance of Ephedra or Welwitschia to that average was determined. Finally, a ratio of these two distances was calculated for each gene for Welwitschia and for Ephedra. Ratios greater than 1, seen for almost every gene, indicate that gnetalean genes are evolving at an elevated rate. For Welwitschia, the average ratio is 1.67, meaning the genes have diverged at 1.67 times the rate of the other seed plants. For Ephedra, this ratio is even higher, at 1.84. For 46 of the 57 genes, the Ephedra ratio is greater than the Welwitschia ratio, indicating that overall genes in the Ephedra genome are evolving even more rapidly than those of Welwitschia.
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1 - Central Washington University, Department of Biological Sciences, 400 E University Way, Ellensburg, WA, 98926-7537, USA
2 - DOE Joint Genome Institute, Department of Evolutionary Genomics, 2800 Mitchell Drive, Walnut Creek, California, 94598, USA
3 - SymBio and UC Berkeley, 1455 Adams Drive, Menlo Park, CA, 94025, USA
Presentation Type: Recent Topics Poster
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM