Résumé
Amborella trichopoda is understood to be the most basal extant flowering plant and its genome is anticipated to provide insights into the evolution of plant life on Earth (see the Perspective by Adams ). To validate and assemble the sequence, Chamala et al. (p. 1516 ) combined fluorescent in situ hybridization (FISH), genomic mapping, and next-generation sequencing. The Amborella Genome Project (p. 10.1126/science.1241089 ) was able to infer that a whole-genome duplication event preceded the evolution of this ancestral angiosperm, and Rice et al. (p. 1468 ) found that numerous genes in the mitochondrion were acquired by horizontal gene transfer from other plants, including almost four entire mitochondrial genomes from mosses and algae. Much of the mitochondrial DNA genome of the flowering plant Amborella trichopoda originated from other organisms. We report the complete mitochondrial genome sequence of the flowering plant Amborella trichopoda . This enormous, 3.9-megabase genome contains six genome equivalents of foreign mitochondrial DNA, acquired from green algae, mosses, and other angiosperms. Many of these horizontal transfers were large, including acquisition of entire mitochondrial genomes from three green algae and one moss. We propose a fusion-compatibility model to explain these findings, with Amborella capturing whole mitochondria from diverse eukaryotes, followed by mitochondrial fusion (limited mechanistically to green plant mitochondria) and then genome recombination. Amborella ’s epiphyte load, propensity to produce suckers from wounds, and low rate of mitochondrial DNA loss probably all contribute to the high level of foreign DNA in its mitochondrial genome.