There is a new paper in
Nature by Bergthorsson et al suggesting that horizontal gene transfer in angiosperms is more common than previously thought. They looked only at the mitcochondrial genomes of several angiosperms, and found several putative examples of HTGs.
Quote:
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Horizontal gene transfer—the exchange of genes across mating barriers—is recognized as a major force in bacterial evolution. However, in eukaryotes it is prevalent only in certain phagotrophic protists and limited largely to the ancient acquisition of bacterial genes. Although the human genome was initially reported to contain over 100 genes acquired during vertebrate evolution from bacteria, this claim was immediately and repeatedly rebutted. Moreover, horizontal transfer is unknown within the evolution of animals, plants and fungi except in the special context of mobile genetic elements. Here we show, however, that standard mitochondrial genes, encoding ribosomal and respiratory proteins, are subject to evolutionarily frequent horizontal transfer between distantly related flowering plants. These transfers have created a variety of genomic outcomes, including gene duplication, recapture of genes lost through transfer to the nucleus, and chimaeric, half-monocot, half-dicot genes. These results imply the existence of mechanisms for the delivery of DNA between unrelated plants, indicate that horizontal transfer is also a force in plant nuclear genomes, and are discussed in the contexts of plant molecular phylogeny and genetically modified plants.
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Bergthorsson et al., Widespread horizontal transfer of mitochondrial genes in flowering plants," Nature, 424:197-201, July 10, 2003.
I predict that both advocates and opponents of transgenic crops will be pointing to this paper quite a bit. The advocates will say somethign: "Look here, gene transfer between species happens all the time in nature. Why can't we do it too?" And the opponents will say something like: "Look here, gene transfer between species happens all the time in nature. So any gene we put in a crop could end up in some other organism's genome, creating who-knows-what kind of effect."
Also, check out the commentary in
The Scientist:
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Horizontal gene transfer (HGT) is the transfer of genetic material between distinct species, a process that plays a major role in the evolution of a genome. There is an increasing body of evidence for the transfer of genes between eukaryotes, but the complexities of transcription and translation regulation in eukaryotes have always been thought to be a barrier to HGT. In the July 10 Nature, Ulfar Bergthorsson and colleagues at Indiana University show that standard mitochondrial genes are subject to frequent HGT between distantly related angiosperms, implying the presence of a mechanism for transfer of DNA between unrelated plants (Nature, 424:197-201, July 10, 2003).
Bergthorsson et al. surveyed the mitochondrial gene content of a number of angiosperms and found distribution anomalies. Phylogenetic analysis of two mitochondrial ribosomal protein genes—rps2 and rps11—resulted in the identification of four cases of plant-to-plant HGT, suggesting that the frequency of HGT is significant. The authors also suggest that previous placements of the atp1 gene should be reclassed as an HGT event. Expression analysis of Sanguinaria indicated that the rps11 RNA is probably functional and that the atp1 gene of Amborella is transcribed and edited. Using molecular-clock–based divergence times, the age of each transfer was also estimated.
"These results establish for the first time that conventional genes are subject to evolutionarily frequent HGT during plant evolution and provide the first unambiguous evidence that plants can donate DNA horizontally to other plants. This is also the best evidence that eukaryotic genomes regularly acquire genes by means of horizontal events that are relatively recent, datable and definable as to donor and recipient," conclude the authors.
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Patrick
07-10-2003, 11:23 AM
'Frequent' horizontal gene transfer in plants
