Tropical forests are home to some of the most diverse and fascinating life forms on Earth. But they also harbor a secret that could change the way we understand and protect them: a rare and hidden genetic diversity that lies within the heart of their trees.
A groundbreaking study published on February 29, 2024, by a team of scientists from INRAE, CIRAD, and CNRS, has revealed the origin and extent of heritable mutations in tropical trees.
These mutations, which occur during the growth of the trees, can be passed onto their seeds and offspring, creating a rich and complex genetic variation that spans generations.
The study, which was conducted in the lush greenery of French Guiana forest, raises pivotal questions about the evolution and adaptation of plants in changing environments.
It also sheds light on the crucial role that tropical trees play in regulating the climate, maintaining biodiversity, and providing resources for local communities.
The Mystery of Mutations(Photo : MARIANA SUAREZ/AFP via Getty Images)
Mutations are changes in the DNA sequence of an organism that can alter its traits and functions. They can be caused by various factors, such as exposure to radiation, chemicals, or viruses, or by errors during DNA replication or repair.
Some mutations are beneficial, giving the organism an advantage in survival or reproduction. Some are neutral, having no noticeable effect. And some are harmful, impairing the organism's fitness or health.
But not all mutations are equal. Some affect only the cells where they occur, such as in the skin or the leaves. These are called somatic mutations, and they are not inherited by the offspring.
Others affect the cells that produce gametes, such as pollen or ovules. These are called germline mutations, and they are transmitted to the next generation.
Germline mutations are the main source of genetic variation in sexually reproducing organisms. They are responsible for creating new alleles, or versions, of genes that can be shuffled and recombined during meiosis and fertilization.
They are also the raw material for natural selection, the process that favors the survival and reproduction of individuals with the most suitable traits for their environment.
But how do plants, especially long-lived and immobile ones like trees, acquire germline mutations? And how do they affect their genetic diversity and adaptation?
These are the questions that motivated the researchers from INRAE, CIRAD, and CNRS to embark on an ambitious and innovative project: to map the mutations in the genomes of tropical trees and trace their origin and transmission.
The researchers chose to focus on two species of tropical trees: Eperua falcata and Symphonia globulifera. These species are native to the Guiana Shield, a region that covers parts of Brazil, Colombia, Venezuela, Guyana, Suriname, and French Guiana.
The researchers collected leaf samples from 234 trees of each species, covering an area of about 10 square kilometers. They also collected seeds from 30 trees of each species, representing three generations of offspring.
They then sequenced the genomes of all the samples, using a technique called whole-genome shotgun sequencing, which allows them to read the entire DNA sequence of an organism.
The results were astonishing. The researchers found that the trees had a very high rate of germline mutations, comparable to that of humans.
They also found that these mutations were mostly caused by errors during DNA replication, rather than by external factors.
And they found that these mutations were not randomly distributed across the genome, but rather clustered in certain regions, called mutational hotspots.
The researchers estimated that each tree had about 5,000 germline mutations, and that each generation of offspring inherited about 2,500 of them.
This means that each tree had a unique genetic signature, and that each generation of offspring had a different combination of mutations from their parents and grandparents.
This remarkable diversity, which was previously unknown, has profound implications for the evolution and adaptation of tropical trees.
It suggests that these trees have a high potential to respond to environmental changes, such as climate change, by generating new variants that can cope with different conditions.
It also suggests that these trees have a high resilience to genetic drift, the random loss of alleles due to small population size or isolation.
The researchers also found that some of the mutations affected genes that are involved in important biological processes, such as photosynthesis, stress response, and disease resistance.
These mutations could have functional consequences for the trees, altering their traits and performance.
The researchers plan to further investigate the effects of these mutations on the phenotype and fitness of the trees, as well as on their interactions with other organisms, such as pollinators, herbivores, and pathogens.