The DNA that the Amborella mitochondria absorbed and retained through horizontal gene transfer amounts to at least one million base pairs, with its mitochondrial genome now swollen to an enormous size of 3.9 million base pairs compared with typical plant mitochondrial genomes sizes of around 500,000. Animal mitochondria virtually stopped this process of gene transfer long ago.
The research provides strong evidence for the hypothesis that plant mitochondria can take up new traits by fusing with the mitochondria of other species. In Amborella, the mitochondria have ample opportunities to come into contact with mitochondria of other plants, for example epiphytes, plants that grow on other plants. When injured, Amborella often generates rapid growth at these locations, a virtual petri dish for mitochondria of different species to come into direct contact with each other. This, coupled with a low rate of losing mitochondrial genes over time, has created Amborella's huge mitochondrial DNA glut.
Palmer cited several motivating factors for plumbing the genomic entrails of Amborella's mitochondria. "Although they contain a relatively small number of genes, plant mitochondrial genomes are disproportionately important in terms of basic metabolism. This is because they encode most of the key proteins involved in respiration." He also pointed to defects in plant mitochondrial genes that can cause cytoplasmic male sterility -- when plants fail to produce functional pollen -- a critically important agronomic trait for hybrid seed production. He said that findings from plant mitochondrial genome studies can also be extrapolated to other mitochondrial genomes, to shed light, for instance, on the mechanisms of cellular aging.
|Contact: David Gilbert|
DOE/Joint Genome Institute