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@ARTICLE{TreeBASE2Ref17354, author = {M. V. Sanchez-Puerta and Yangrae Cho and J. P. Mower and Andrew J Alverson and Julie Gummow and Jeffrey D. Palmer}, title = {Horizontal transfer of cox1 group I intron among flowering plants: assessing the variation in the coconversion tract}, year = {2008}, keywords = {}, doi = {}, url = {}, pmid = {}, journal = {BMC Evolutionary Biology}, volume = {}, number = {}, pages = {}, abstract = {Horizontal gene transfer (HGT) is surprisingly common among plant mitochondrial genomes. The first well-established case of HGT in plants involves a group I intron in the mitochondrial cox1 gene. The highly sporadic presence of the intron across angiosperms, strongly supported conflicts between organismal and intron phylogenies, and evidence from coconversion tracts combine to suggest frequent horizontal transfer of the cox1 intron aided by the intron-encoded, site-specific endonuclease. Here we report extensive additional sampling of angiosperms, including discovery of 92 newly sequenced introns from 43 families. Analysis of all available data leads us to conclude that, among the 686 angiosperms whose cox1 intron status has been characterized thus far, the intron has been acquired by approximately 60 separate horizontal transfer events. Extended sampling of three families (Marantaceae, Rhamnaceae, Rubiaceae) reveals what appears to be surprisingly frequent transfer between members of the same family, while a similar conclusion was published in an earlier study on the Araceae. Illegitimate pollination is proposed as the responsible mechanism, given that cross-species pollination is more likely between relatively close relatives. The first cases of apparent loss of the cox1 intron are reported; these are accompanied by either retention or loss of the exonic coconversion tract located in exon 2, immediately downstream of the intron and itself a product of the introns self-insertion mechanism. We propose three possible hypotheses to explain the presence of different length coconversion tracts among close relatives with highly related intron sequences. One hypothesis posits multiple intron transfers among these closely related plants, with limited exonucleolytic degradation in exon 2 at the time of transfer leading to shortened coconversion tracts. Second, partial conversion of exon 2 with a foreign, intronless allele of cox1 could erase part of the coconversion tract. Third, lineage sorting could lead to differential transmission of polymorphic coconversion tracts tracing back to the introns original establishment within a founder plant to species within a clade of strictly vertically transmitted intron sequences.} }