The Wollemi pine was thought to have become extinct 2 million years ago until it was rediscovered by a group of tourists in 1994. Now scientists have decoded its genome to understand how it has survived virtually unchanged since the time of the dinosaurs. In 1994, hikers discovered a group of strange trees growing in a canyon in Wollemi National Park, about 100 kilometers west of Sydney, Australia. One of the hikers reported this to a park service naturalist, who showed the leaf samples to a botanist. It was eventually decided to represent an ancient species that had been frozen in time since dinosaurs roamed the Earth.

Wollemi pine (wollemia nobilisThe fossil, which some call a “living fossil,” is nearly identical to preserved remains dating to the Cretaceous period (145 to 66 million years ago). There are currently only 60 such trees in the wild, and they are threatened by forest fires in the region. They were thought to have become extinct about 2 million years ago.

Now scientists from Australia, the US and Italy have deciphered its genome, shedding light on its unique evolution and breeding habits and aiding conservation efforts. The paper was published in the bioRxiv preprint database on August 24 and was not peer-reviewed.

The pine tree has 26 chromosomes containing 12.2 billion base pairs. By comparison, humans only have about 3 billion base pairs. Despite their genome size, Wollemi pines have extremely low genetic diversity; This suggests a bottleneck around 10,000-26,000 years ago (during which the population declined significantly).

In fact, plants do not exchange much genetic material. The rest of the trees appear to reproduce mainly by cloning via sprouts; suckers emerge from the base and grow into new trees.

Their rarity can be partly explained by the large number of transposons, or “jumping genes” (extensions of DNA that can change their position in the genome). These elements also determine the size of the genome. “The smallest plant genome and the largest plant genome have almost the same number of genes. Large differences in size are often caused by transposons.”said Gerald Schenknecht, program director for the National Science Foundation’s Plant Genome Research Program. Schenknecht was not involved in the research, but NSF provided funding.

When transposons move to new locations, they can change the sequence of “letters” in the DNA molecule, thus causing or altering mutations in genes. They can carry functional DNA with them or modify DNA at the point of entry and thus have a significant impact on the evolution of the organism.

If transposons caused harmful mutations, they may have contributed to population declines due to climate change and other factors, the researchers said. These stressful conditions may force the plant to switch to clonal propagation. Since the increase in transposons is associated with sexual reproduction, the change in asexual reproduction may have reduced the potential introduction of deleterious mutations. Paradoxically, although trees still depend on sexual reproduction, transposons may have played a role in increasing genetic diversity, thus making them more resilient to changing conditions, at least temporarily.

“99% of mutations are probably not a good idea”Schenknecht said: “But that 1% that has helped over millions of years may have helped the species advance. In that case, it might have a bit of an advantage.”.

Sequencing the genome also revealed why the Wollemi pine is susceptible to diseases. Phytophthora cinnamomia pathogenic water mold that causes dieback. A tree’s disease resistance genes are suppressed by a type of its own RNA that is associated with the development of larger leaves. Wollemi pines have broad needles, unlike most conifers.

Therefore, the evolution of broader leaves may have resulted in suppression of disease resistance, opening the species to pathogenic threats that could be inadvertently pursued by travelers illegally visiting a protected area. P. cinnamon It is common among cultivated plants.

Although only four small populations remain in the wild, pines are actively propagated by botanical gardens and other institutions to protect them and study their unique biology. According to IUCN This species is endangered. Therefore, analyzing the Wollemi pine genome is not just a scientific curiosity; It also has serious consequences for the survival of the species. Source