Multiple Horizontal Transfers and Partial Recombination of cox1 Exons in Plant Mitochondria

SÁNCHEZ PUERTA, M. V. & J.D. PALMER.

Evry, Francia

Conferencia; Plant genomics and Beyond Conference; 2009

INRA

Horizontal gene transfer (HGT) is extensive in prokaryotes and, to a lesser extent, in unicellular eukaryotes. Recently, however, HGT involving multicellular eukaryotes has been increasingly reported. Most notably, HGT among flowering plants has been shown to be a more widespread phenomenon than previously thought possible. Most cases involve mitochondrial sequences (introns or genes) that are transferred to the mitochondrial genome of another angiosperm. Until now, most cases of HGT in plant mitochondria have been of duplicative HGT. Little is known about the expression and functional implication of these horizontally transferred genes. We analyzed cox1 sequences from more than 400 angiosperms and found that seven unrelated lineages of flowering plants shared a stretch of 15 nucleotides while virtually all others show a conserved sequence. The sporadic and uneven distribution of this “motif” can be explained by horizontal transfer of the cox1 gene, followed by partial conversion with the native copy. Phylogenetic analyses of the cox1 exons find conflicting relationships with the known organismal phylogeny. In addition, the cox1 gene has been invaded several times by a group I intron that has been transferred multiple times among angiosperms. This is the first case of a functional HGT, in which a chimeric gene is formed bringing 3 amino acid replacements to the protein and it is expressed. Because the cox1 gene is the only mitochondrial gene that has not been functionally transferred to the nuclear genome, the mitochondrial-encoded chimeric cox1 gene is most likely the only functional gene copy.