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Early Transfer of DNA from Insects to Pines

Photo of FISH with Dryad DNA probe on loblolly pine chromosome spread showing the distribution of Dryad elements on the pine genome (scattered red signals). The green signals are from ribosomal rDNA (18S-28S rDNA). Insert is an interphase nucleus. Nurul Faridi, U.S. Department of Agriculture Forest Service.FISH with Dryad DNA probe on loblolly pine chromosome spread showing the distribution of Dryad elements on the pine genome (scattered red signals). The green signals are from ribosomal rDNA (18S-28S rDNA). Insert is an interphase nucleus. Nurul Faridi, U.S. Department of Agriculture Forest Service.Snapshot : Repetitive DNA sequences move across species boundaries relatively often, but rarely occur between kingdoms; however, Forest Service scientists and partners have identified and characterized such a transfer between insects and conifers and determined that it occurred about 340 million years ago. They concluded that this sequence was one of the oldest transfers and the only known transfer that has occurred between animals and plants.

Principal Investigators(s) :
Nelson, C. Dana 
Research Station : Southern Research Station (SRS)
Year : 2016
Highlight ID : 1098

Summary

Whole genome DNA sequencing is the key technology in studying the evolution of gene structure and function. Such efforts will be instrumental in guiding breeding programs needed to face the growing food, feedstocks and fiber demands of the 21st century. Forest Service scientists at the agency’s Southern Research Station recently sequenced the genome of loblolly pine, and used this data to delve further into the pine genome's details. They found that a group of repetitive DNA sequences had been transferred from insects to a common ancestor of the pines, spruces, and other conifers, about 340 million years ago, but not to any other trees. The sequences are known as Penelope-like transposable elements, or Dryad elements. Further analysis from 1,928 genomes of 14 major lineages showed that there was no evidence of the Dryad elements outside of animals and conifers. Transposable elements can be thought of as genomic parasites, because once they invade a genome they become highly active at making new copies of themselves resulting in marked increases in the species' DNA content. Most organisms have genetic mechanisms to reject foreign DNA or shut down the multiplication activity of the foreign sequences; however, in the case of a newly evolving species, where the defense mechanism has not fully developed, the foreign DNA can make hundreds of thousands of copies that can persist in the host species' genome for millions of years. In these cases, the foreign DNA is likely to cause structural changes to their host genomes that can affect the function of nearby genes. The Dryad elements likely had significant influence in the genomes of ancestral conifers and could still be influencing the genome of present day conifers, such as loblolly pine. Nonetheless, future research is needed to understand how conifer chromosomes and genes are affected by these DNA sequences since their presence is an important indicator of past and future evolution.

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