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Some of the trees that populate the Earth today are older than the Egyptian pyramids and have witnessed the last 5,000 years of human history.
A team of scientists has sequenced the oak genome, which spans three continents, to understand what lies behind its long life. The study shows that the immune system plays a key role in ensuring its centuries-old survival.
The seventeenth century witnessed the birth of Isaac Newton, one of the most important scientists in history, author of the law of universal gravitation. In the shadow of this English physicist and mathematician, some oaks came to light that are still alive today, 350 years later. But they are not unique.
In 1965, a study published in the journalEcology by geologist Donald Currey allowed us to find the oldest tree in the world until then: a Colorado pine (Pinus aristata) of 4,844 years in the Nevada mountains in the US The tree, nicknamed Prometheus, was felled by mistake.
Since then, protection measures have increased and the ranking of long-lived trees has expanded. Prometheus is now followed by two copies ofPinus longaevathat occupy the first two positions, one called Methuselah of 4,845 years old and another of an unknown name of about 5,062 years, from the White Mountains of California. And the question arises: how can these living beings live for so many years?
An international team of scientists, led by Christophe Plomion, from the University of Bordeaux in France and with the participation of the University of Gerona, reveals that the long lifespan of trees could be explained by the spread of disease-resistant genes. The study, published inNature Plants, would explain how some trees can survive for centuries despite adversity.
The case of oak, under study
The researchers focused on the common oak (Quercus robur), a tree that has 450 species spread across Asia, Europe and America, and which has become a cultural emblem due to its ubiquity and longevity. To do this, they sequenced the genome of this tree and compared it with the whole genome sequences of other plants.
The results show that oak underwent a massive explosion of gene duplication in tandem (in regions that lie side by side). The accumulation of somatic mutations appears to have contributed to 73% of the expansion of the total oak gene family. These are largely associated with disease resistance genes and exhibit positive selection signatures.
"This work raises new questions about the contribution of this mutational burden to adaptation, particularly with regard to defenses against new pests and pathogens," the authors say in the study. According to the researchers, the immune system makes an essential contribution to the survival of long-lived plants for several centuries.
The scientists also found similar expansions of the disease resistance gene in other tree genomes.
Christophe Plomion et al. "Oak genome reveals facets of long lifespan"Nature Plants June 18, 2018