Plant DNA Largely Unchanged

Today’s tulip trees carry similar mitochondrial DNA as those that grew in the time of the dinosaurs.

Apr 15, 2013
Jef Akst

The tulip tree (Liriodendron tulipifera) BIOMED CENTRAL, GARY COTEThe mitochondrial genome of the tulip tree (Liriodendron tulipifera), known to be one of the slowest evolving plant genomes, retains many of the ancestral traits lost by other flowering plants over the last 200 million years of evolution, according to research publishing this week in the open access journal BMC Biology. The newly sequenced genome could thus serve as a critical tool in understanding the evolution of flowering plants, the authors argue.

In plants, the lack of ancient genomic data has made evolutionary reconstruction difficult. So the researchers compared genomes of two flowering plants—Magnolia stellate and Calycanthus floridus—with that of the slow-to-evolve L. tulipifera to reconstruct the frequency of genetic changes in flowering plants in general. They confirmed the Liriodendron mitochondrial genome’s exceptionally slow rate of evolution—“with the lowest known genome-wide absolute silent substitution rate,” they wrote—and identified in its DNA several features inferred to have been present in the ancestral flowering plant mitochondrial genome, including all 41 protein-coding and three rRNA genes, 13 intact mitochondrial tRNAs, and seven tRNAs derived from chloroplasts.

“Based on this, it appears that the genome has been more-or-less frozen in time for millions and millions of years,” lead author Jeffrey Palmer said in a press release.

This ancestral state of the Liriodendron mitochondrial genome could be key to unraveling the evolution of flowering plants, the authors said. “Although nearly 40 flowering plant mitochondrial genomes have been sequenced to date, the addition of Liriodendron, because of its phylogenetic position and extraordinary level of sequence and gene-cluster conservation, greatly refines our view of the ancestral angiosperm mitochondrial genome,” they wrote. “Genomic data from additional ‘early diverging’ angiosperms, such as Nymphaea and Amborella, will provide more detailed insights into mitochondrial genome evolution in early angiosperms.”