In 1994, hikers discovered a group of strange trees growing in a valley in Wollemi National Park, about 60 miles (100 km) west of Sydney, Australia. One hiker notified a Park Service naturalist, who then showed leaf samples to the botanist. It was eventually determined that they represented an ancient species that had essentially been frozen in time since dinosaurs roamed the Earth.
Called a “living fossil” by some, the Willemme pine (Williamia nobilis) is almost identical to preserved remains dating back to the Paleolithic Cretaceous period (145 million to 66 million years ago). There are now only 60 of these trees left in the wild, and these stubborn survivors are threatened by forest fires in the region. He was It is believed to be extinct About 2 million years ago.
Now, scientists from Australia, the United States and Italy have done just that Decode its genome, highlighting their unique development and reproductive habits, as well as aiding conservation efforts. The paper was published in the preprint database bioRxiv on August 24 and has not been peer-reviewed.
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Pine He has 26 chromosomes It contains an amazing 12.2 billion base pairs. In comparison, humans only have about 3 billion base pairs. Despite the size of their genome, willem pines are extremely low in genetic diversity, suggesting the existence of a bottleneck (when populations declined dramatically) about 10,000 to 26,000 years ago.
In fact, plants do not exchange much genetic material. The remaining trees appear to reproduce mostly by cloning themselves through cutting, where the suckers emerge from the base and become new trees.
Their rarity may be due in part to the large number of transposons, or “jumping genes” – stretches of DNA that can change their location within the genome. These elements also represent the size of the genome. “The smallest plant genome and the largest plant genome have roughly the same number of genes,” Gerald Schoenknecht, director of the National Science Foundation’s Plant Genome Research Program, told Live Science. “The large differences in size usually come from transposons.” Schönknecht was not involved in the research, but the National Science Foundation provided funding.
like Transposons By jumping to new positions, they can change the sequence of “letters” in the DNA molecule, thus causing or reversing gene mutations. They may carry with them functional DNA or DNA changes at the insertion site, thus having a major impact on the evolution of the organism.
If transposons cause harmful mutations, they may have contributed to population declines due to climate change and other factors, the researchers said. These stressful conditions may have prompted the plant to switch to clonal reproduction. Since increases in transposons are associated with sexual reproduction, the change in asexual reproduction may have reduced the possibility of them introducing deleterious mutations. Paradoxically, while trees were still dependent on sexual reproduction, transposons may have played a role in increasing genetic diversity, thus making them at least temporarily more resilient to changing conditions.
“In 99% of all cases, mutations are probably not a good idea,” Schocknecht said. “But over millions of years, the 1% that helps can push a species forward. In this case it may have been a bit of an advantage.”
Decoding the genome has also revealed why Wollemi pine is so susceptible to disease – in particular, Phytophthora cinnamomiIt is a pathogenic water mold that causes dieback. The tree’s disease-resistant genes are repressed by a type of RNA that is associated with the development of wider leaves. Lime pines, unlike most conifers, have broad needles.
Therefore, the development of wider leaves may have suppressed disease resistance and opened the species to pathogenic threats – which may have been inadvertently tracked in by hikers who visited the protected area illegally. P. cinnamomi Common in cultivated plants.
Although only four small populations remain in the wild, pines have been widely propagated by botanical gardens and other institutions in an effort to conserve them and study their unique biology. This species is considered critically endangered By the International Union for Conservation of Nature.
Hence, analyzing the genome of the Wollemi pine is not just an academic curiosity, but has serious implications for the survival of this species.
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