Ancient Bristlecone Pines May Hold Clues for Longevity

What can the world’s longest living individual teach us about living a very long time? A team of scientists coordinated by the University of California, Davis, sequenced the genome of the Great Basin bristlecone pine, which could help unlock the secrets of this tree’s exceptional longevity and provide insights for other species.

Their study, published in the journal G3: Genes|Genomics|Genetics, notes that the Great Basin bristlecone pine, Pinus longaeva, is the oldest individual, non-clonal organism on the planet, with some trees living more than 5,000 years. “Pando,” a giant colony of aspen stems that originate from a single root system, is estimated to be older. However, its individual stems are rarely more than a few hundred years old.

Wind-sculpted and solitary, with gnarled, twisting branches, the bristlecone pine spends its long life atop some of the harshest, highest and coldest parts of the West. The species is endemic to the Great Basin mountains of eastern California, Nevada and Utah and typically grows at elevations between 9,500 and 11,800 feet.

With a permit from the United States Department of Agriculture's Forest Service, researchers collected tissue samples from the needles and seeds of a bristlecone pine tree in the White Mountains of central-eastern California. Scientists used that material to understand the pine’s entire genetic map. But, how can that help us understand longevity in other species? 

“That’s the secret to understanding any organism,” said project lead David Neale, a professor emeritus in the UC Davis Department of Plant Sciences; he previously helped sequence the coast redwood, giant sequoia and whitebark pine genomes.

The genome, Neale explained, is “like having a parts list. … Having a reference genome (for bristlecone pine) … is now a resource from which modern genetic discovery can begin.”

The papers’ authors added: “We expect this resource to be used not only by forest tree researchers and land managers, but also by the broader scientific community seeking to understand the genetic basis of longevity in all forms of life.”

Their research was funded by the Vaughn-Jordan Foundation through the Whitebark Pine Ecosystem Foundation, as well as by the National Science Foundation and National Institutes of Health. Authors of the study include Patrick McGuire, a genomics project manager in the UC Davis Department of Plant Sciences.

Matters of life and death

The bristlecone pine is not a threatened or endangered species, although extreme heat, drought and bark beetles have contributed to the deaths of some of the trees. But the authors note that the species has persisted for millennia through extreme climate periods in the past. 

“That bristlecone pine has endurance to persist in the face of impacts from climate change is witnessed by the White Mountains populations, which have thrived in place throughout climate extremes for almost 11,000 years – since the last ice age,” said coauthor Constance Millar, an ecologist with the Forest Service’s Pacific Southwest Regional Station. 

A genome sequence for the species can help land managers identify genetic materials that may help these trees adapt to future environments.

Could this work help other species live longer, too? 

“People ask me those kinds of things: ‘David, tell me which is the longevity gene, and I will clone it, patent it and sell it.’ Of course, it’s massively complex. But there could be some fundamental discovery of the genetic basis of longevity in this one organism that could be applied to other organisms,” Neale said. 

For instance, one theory is that bristlecone pines may not “senesce,” or biologically age and die. Human cells, no matter how well we care for ourselves, eventually die and are not replaced, leading to death. But bristlecone pine trees do not appear to hold the signatures of senescence. Their deaths tend to be caused by outward forces – an axe or a fierce storm – but not by old age alone. Could they potentially live forever?

“That theory is overstated, but you can’t help but have those thoughts when you look at something that can live that long,” Neale said. “Maybe, by having an equivalent study in something that lives to be 5,000 years versus something — or someone — that lives to be 100 could be informative. 

“Maybe not. It could be the bristlecone pine tree is fundamentally unique, and nothing lives to be like it.”

Long telomeres and 'junk' DNA

Scientists at Johns Hopkins University conducted genetic sequencing on the samples the team collected. They found 21,364 protein-coding genes, including genes showing disease resistance and larger-than-average telomere lengths, compared with other conifers. Large telomeres typically signify a longer cell life and slower aging. (Telomeres are special sequences of molecules at the ends of chromosomes that prevent the loss of vital genes when a cell’s DNA divides. The degradation of telomeres is associated with age-related illness.)

“Assembling a 24-billion-base-pair genome that is eight times the size of the human genome is a significant technical challenge," said co-author Steven Salzberg, a professor of biomedical engineering at Johns Hopkins University.

"Despite its great size, though, the genome of bristlecone pine contains only slightly more genes than the human genome. The rest of the genome is filled with millions of repetitive 'junk DNA' sequences, which appear to do no harm to the organism, since it has carried these repeats through millions of years of evolutionary history."

Related links

Read their paper here: “Genome Report: A reference genome sequence for the exceptionally long-lived Great Basin bristlecone pine, Pinus longaeva.”