In 1994, a remarkable discovery unfolded as hikers stumbled upon a cluster of peculiar trees nestled within a canyon in Wollemi National Park, located approximately 60 miles (100 kilometers) west of Sydney, Australia. One vigilant hiker promptly alerted a park service naturalist, who, in turn, sought the expertise of a botanist. The subsequent examination of leaf specimens yielded a remarkable revelation: these enigmatic trees represented an ancient species, virtually untouched by time since the era when dinosaurs roamed the Earth.
Referred to by some as a “living fossil,” the Wollemi pine, scientifically known as Wollemia nobilis, bears an uncanny resemblance to fossilized remains dating back to the Cretaceous period, spanning from 145 million to 66 million years ago. Astonishingly, today, merely 60 of these trees persist in the wild, clinging to survival amidst the looming threat of bushfires. Remarkably, it was believed to have gone extinct nearly 2 million years ago.
A collaborative effort between scientists hailing from Australia, the United States, and Italy has now culminated in the decoding of the Wollemi pine’s genome, an endeavor that promises to illuminate its unique evolutionary journey, reproductive mechanisms, and, most importantly, facilitate conservation initiatives. The findings from this study have been published on the preprint database bioRxiv, although they have yet to undergo peer review.
The genome of the Wollemi pine presents an awe-inspiring complexity, boasting an astounding 26 chromosomes that harbor an astonishing 12.2 billion base pairs. In comparison, the human genome comprises a relatively modest 3 billion base pairs. Despite this staggering genetic scale, Wollemi pines exhibit an unexpectedly low genetic diversity, indicative of a bottleneck event that occurred between 10,000 to 26,000 years ago.
Curiously, these enigmatic plants exhibit limited genetic exchange, largely relying on a clonal mode of reproduction facilitated through coppicing, where new trees sprout from suckers emerging at the base.
The rarity of the Wollemi pine species can be partially attributed to the abundance of transposons, colloquially referred to as “jumping genes.” These are stretches of DNA that have the capacity to relocate within the genome. These transposons are also responsible for the substantial size of the pine’s genome. “The tiniest plant genome and the largest plant genome have almost the same number of genes. Large differences in size usually come from transposons,” explains Gerald Schoenknecht, program director for the National Science Foundation’s Plant Genome Research Program, although he was not directly involved in this research.
Transposons hold the remarkable ability to induce alterations in the DNA molecule’s sequence, thereby causing or reversing mutations in genes. These elements can carry functional DNA or modify DNA at the site of insertion, significantly influencing an organism’s evolutionary trajectory.
Intriguingly, the surge in transposon activity and its correlation with sexual reproduction in the Wollemi pines could have potentially exacerbated harmful mutations. These detrimental mutations may have contributed to a population decline precipitated by changing climatic conditions and other external factors. It is conceivable that these unfavorable conditions may have prompted the plant to pivot towards asexual reproduction. This shift in reproductive strategy, albeit paradoxical, may have temporarily bolstered resilience to evolving environmental pressures.
Notably, the Wollemi pine’s genome analysis has unveiled insights into its vulnerability to disease, particularly Phytophthora cinnamomi, a pathogenic water mold known to cause dieback. The tree’s innate disease-resistant genes appear to be subdued by a specific RNA variant linked to the development of broader leaves. Unlike most conifers, Wollemi pines sport wider needles, an evolutionary trait that may have inadvertently suppressed their disease resistance mechanisms. Regrettably, the broader leaves may have rendered the species more susceptible to pathogenic threats, a peril compounded by the unauthorized visits of hikers who unwittingly introduced Phytophthora cinnamomi to the protected area. This pathogen is commonplace in cultivated plants.
While a mere four small populations endure in the wild, extensive efforts have been undertaken by botanic gardens and research institutions to propagate the Wollemi pine, with a dual aim of conserving this critically endangered species and unraveling its extraordinary biology. The Wollemi pine’s genome analysis extends beyond academic curiosity; it carries profound implications for the species’ very survival.