Widespread horizontal transfer of mitochondrial genes in flowering plants

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Abstract
Horizontal gene transfer—the exchange of genes across mating barriers—is recognized as a major force in bacterial evolution1,2. However, in eukaryotes it is prevalent only in certain phagotrophic protists and limited largely to the ancient acquisition of bacterial genes3,4,5. Although the human genome was initially reported6 to contain over 100 genes acquired during vertebrate evolution from bacteria, this claim was immediately and repeatedly rebutted7,8. Moreover, horizontal transfer is unknown within the evolution of animals, plants and fungi except in the special context of mobile genetic elements9,10,11,12. 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.