Abstract:We report the complete mitochondrial genome sequence of the flowering plant Amborella trichopoda. This enormous, 3.9 Mb 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.

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Why have some plants lost the organizational stability in plastid genomes (plastomes) that evolved in their algal ancestors? During the endosymbiotic transformation of a cyanobacterium into the eukaryotic plastid, most cyanobacterial genes were transferred to the nucleus or otherwise lost from the plastome, and the resulting plastome architecture in land plants confers organizational stability, as evidenced by the conserved gene order among bryophytes and lycophytes, whereas ferns, gymnosperms, and angiosperms share a single, 30-kb inversion. Although some additional gene losses have occurred, gene additions to angiosperm plastomes were previously unknown. Plastomes in the Campanulaceae sensu lato have incorporated dozens of large ORFs (putative proteincoding genes). These insertions apparently caused many of the 125+ large inversions now known in this small eudicot clade. This phylogenetically restricted phenomenon is not biogeographically localized, which indicates that these ORFs came from the nucleus or (less likely) a cryptic endosymbiont.foreign DNA | Cyphiaceae | Lobeliaceae | phylogeny T he extant diversity of algae and land plants chronicles the ongoing endosymbiotic transformation of a cyanobacterium into eukaryotic plastids (1), which are commonly known as chloroplasts because of their primary photosynthetic function. The early steps in plastome evolution involved the loss or transfer to the nucleus of most cyanobacterial genes, but an intron maturase (matK) and the two largest genes [ycf1 (an inner membrane translocon component); ref.2) and ycf2 (still of unknown function)] were incorporated before the origin of land plants (3). The characteristic plastome architecture of land plants (Fig.

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Chloroplast DNA restriction-site variation was surveyed among 40 accessions representing all 11 species of giant senecios (Dendrosenecio, Asteraceae) at all but one known location, plus three outgroup species. Remarkably little variation (only 9 variable sites out of roughly 1000 sites examined) was found among the 40 giant senecio accessions, yet as a group they differ significantly (at 18 sites) from Cineraria deltoidea, the closest known relative. This pattern indicates that the giant senecios underwent a recent dramatic radiation in eastern Africa and evolved from a relatively isolated lineage within the Senecioneae. Biogeographic interpretation of the molecular phylogeny suggests that the giant senecios originated high on Mt. Kilimanjaro, with subsequent dispersion to the Aberdares, Mt. Kenya, and the Cherangani Hills, followed by dispersion westward to the Ruwenzori Mountains, and then south to the Virunga Mountains, Mt. Kahuzi, and Mt. Muhi, but with dispersion back to Mt. Elgon. Geographic radiation was an important antecedent to the diversification in eastern Africa, which primarily involved repeated altitudinal radiation, both up and down the mountains, leading to morphological parallelism in both directions. In general, the plants on a given mountain are more closely related to each other than they are to plants on other mountains, and plants on nearby mountains are more closely related to each other than they are to plants on more distant mountains. The individual steps of the geographic radiation have occurred at various altitudes, some clearly the result of intermountain dispersal. The molecular evidence suggests that two species are extant ancestors to other species on the same or nearby mountains.The giant senecios are an unusual group of plants that have diversified to occupy a range of habitats, from 2500 to 4600 m, on 10 mountains >3300 m tall within 40 of the equator in Zaire, Rwanda, Uganda, Kenya, and Tanzania (1). Now segregated as the genus Dendrosenecio (Hauman ex Hedberg) Nordenstam, the giant senecios comprise 11 species and 6 nonautonymic subspecific taxa (2). Their habitats range from upper montane forest (mist-forest) through the giant heather zone and highaltitude wet meadows and extend almost to the upper limit of the unusual afro-alpine zone, whose climate has been characterized as "summer every day and winter every night" because strong diurnal fluctuations exceed seasonal variation (3). These plants typically have a giant-rosette growth form with a massive terminal leaf rosette borne atop a thick woody stem. During reproduction, a large terminal inflorescence is produced, and two to four lateral branches are usually initiated. Old plants appear as candelabras the size of telephone poles, with each branch bearing a leaf rosette (Fig. 1). The giantrosette growth form, large pith volume, marcescent foliage, and nyctinasty have evolved independently in the montane east The giant senecios show an unusual trend of massive plants occurring at high elevations, with smaller plan...

With adequate molecular and taxon sampling, many details of rapid radiations can be accurately inferred. However, not all lineages survived, and analyses of extant species cannot recover details that have been lost due to extinction.

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