Systematics/Phytogeography / Taxonomie/ Section
Lackey, Kelli , Raubeson, Linda A. .
Does the plastid inverted repeat loss support conifer monophyly?
The placement of the gnetales within the seed plants, and therefore the monophyly of conifers, is debated. Gnetales are often associated with conifers in molecular phylogenies, sometimes as the sister to conifers and other times placed within conifers as the sister to Pinaceae (the “gne-pine” hypothesis). The exclusion of gnetales from conifers has been supported by the loss of the large inverted repeat (IR) from all investigated conifer plastomes but from no examined gnetalean plastomes. The distribution of this trait opposes the gne-pine hypothesis unless the IR has been lost independently in the two major lineages of conifers. Looking at the current gene arrangements of our complete plastome sequences of Cryptomeria japonica and Podocarpus macrophyllus and the published plastome of Pinus thunbergii, two separate IR losses seem at least superficially possible with Cryptomeria japonica and Podocarpus macrophylla losing the IR copy between psbA and chlL and Pinus thunbergii losing the copy between the S10 operon and ndhF. However, because each of the conifer genomes contains multiple other gene order changes, current adjacencies could be misleading. We investigated the total number of rearrangement mutations (inversions and IR loss(es)) required to achieve the gene orders of the extant conifers under alternative hypotheses of IR loss to see if significantly fewer mutations are required under a particular scenario. Unfortunately, the number of mutations necessary, under the different hypotheses requiring one IR loss or two, does not provide strong support for one hypothesis over another – each hypothesis required either 20 (for one hypothesis of two separate losses) or 21 total changes (for other hypotheses of separate losses and all hypotheses of one shared loss). Therefore the monophyly of the conifers cannot be supported or refuted by the IR loss distribution using this logic.
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1 - Central Washington University, Biological Sciences, 400 E. University Way, Ellensburg, WA, 98926-7537, U.S.A.
2 - Central Washington University, Department of Biological Sciences, 400 E University Way, Ellensburg, WA, 98926-7537, USA
Presentation Type: Poster:Posters for Sections
Location: Ball Room & Party Room/SUB
Date: Monday, July 28th, 2008
Time: 12:30 PM