From fungi to plants, a 500-million-year-old gene transfer at the origin of our ecosystems

The terrestrial ecosystems in which we live today are the result of a major transition that took place 500 million years ago :
algae emerged from the waters and reached the emerged land. Since that key moment, they have progressively evolved into an immense diversity of terrestrial plants, which have partly been domesticated by humans for food production. The in-depth study of plants of agronomic interest has led to an almost exclusive focus on flowering plants. However, while most plant science research is focused on this group, it represents only a small portion of terrestrial plant diversity.

There's another group of plants, the bryophytes, “whose common ancestor with flowering plants lived on earth 500 million years ago”, explains Maxime Bonhomme, lecturer at the University of Toulouse and co-author of the study. “We undertook to analyze the genetic background of a hundred individuals of a specific bryophyte species, Marchantia polymorpha - the fountain liverwort - from both Europe and the United States.”

Among the different gene families identified by scientists, there is one that particularly stands out as it results from a transfer from a fungus to the common ancestor of terrestrial plants. Transmitted at the time when algae were emerging from the water, this gene may have had a major impact.

“Our work shows that this gene is associated with adaptation to the terrestrial environment, and we can speculate that without it, algae would not have been able to remain on land for very long. This gene may have enabled them to adapt to the new constraints of their open-air habitat : lack of water, encounters with new microorganisms...” adds Pierre-Marc Delaux, CNRS research director and co-author of the article.

In their analyses, the scientists also found important receptors for the plant immunity that enables it to resist diseases, as well as proteins responsible for the oxidative balance in cells, an essential response to resist the environmental constraints.
These functions are already well known in the stress response of several flowering plants, “but what is remarkable is that they were already present in their common ancestor, and have been preserved throughout the hundreds of millions of years of evolution and diversification of the plant kingdom”, according to Pierre-Marc Delaux.

This study reveals that horizontal gene transfer - the integration of genetic material from one organism by another of which it is not the descendant - has played a more important role than previously thought in the adaptation of plants to terrestrial life.
 

For Chloé Beaulieu, PhD student at the University of Toulouse and first author of the study, “this discovery would never have been possible if we had limited ourselves to the plants traditionally studied”. Marchantia polymorpha, a species - like many others - often neglected in scientific literature, demonstrates the importance of extending knowledge beyond the plants of choice in agronomy, in order to obtain a global vision of the evolution of living world and their capacity to adapt.