A “friendship” clearly formed the basis of the Green Revolution on our planet: Researchers present new evidence that the country’s colonization of plants was possible through a symbiotic relationship with the fungus about 450 million years ago. They were able to show that ordinary liverworts – considered living fossils – provide lipids as “commercial goods” to their fungal partners – similar to highly developed plant species. In the case of algae, however, there is no compatible lipid biosynthesis. This leads scientists to conclude that this system dates back to the time when the first plants greened the country in collaboration with their mushroom partners.
Most of today’s plant species have loyal mates: they enter into a close exchange relationship with fungal species living in the soil, through which they can obtain additional nutrients and water from the soil. In this so-called mycorrhizal symbiosis, partners exchange nutrients through connections between extensive fungal networks in soil and plant roots. In the most general form, “trade” occurs through a complex structure inside the roots: the fungus enters them with its hype and forms a tree-like structure (arbuscle) in some cells along with the plant. Then the transfer of nutrients is done to the large surface of this structure. The fungus gives the plant water and, above all, the phosphate, which it has absorbed from the soil. In return, the plant supplies it with energy-rich materials. Studies have shown that in addition to sugar molecules, lipids are also involved.
Pioneers recipe for success?
In the early 1980s, studies of plant fossils revealed that mycorrhizal symbiosis is ancient. It aroused suspicion that the partnership made it possible for plants to go ashore about 450 million years ago: in their new, hardy habitat, the fungi were probably able to provide pioneer plants with water and nutrients in a significant way . The current study by researchers led by Melanie Rich of the University of Toulouse supports this notion with genetic and molecular biological evidence.
They produce long-term research results on genetic makeup that enable plants to enter into complex interrelationships with fungi. Until now, the focus has been on modern vascular plants (tracheophytes) such as beans, potatoes, and the like. But Rich and his colleagues have now devoted themselves to plants that still resemble the pioneers of the plant-based coast recess: mosses (bryophytes). They are believed to have evolved from green algae in the intertidal zone 450 million years ago.
It is known that these primitive plants can also partner with fungi – but the genetic and molecular basis of these fungi-moss symbiosis has not yet been discovered. As part of their study, researchers have now looked at Liverwort Merchantia palesia as a model that forms an arbuscular mycorrhizal symbiosis with a fungus. Using genetic and molecular biological methods, the team has investigated which hereditary factors and processes in plants become active when tree-like exchange structures are produced in their cells and come into action.
They were able to prove that lipids are also transferred from the plant to fungi in liverworts. Researchers were able to clarify that this is the same basic principle of lipid transfer as it is in modern vascular plants. Along with these, the process is also a prerequisite for Kai to be able to create symbiosis. Researchers were able to show this on genetically modified moss breeding lines, in which they discontinued the genetic makeup required for lipid transfer. Studies have shown that these small plants can no longer establish partnerships with fungi.
Researchers were also able to clarify that the lipid biosynthesis system of vascular plants and mosses required for symbiosis is not present in aquatic algae, from which green-land precursors are believed to have once emerged. In these results you see a clear indication that the development of mycorrhizal symbiosis was at the beginning of the history of development of land plants and likely represents a prerequisite for the successful conquest of new habitat. “Our results suggest that the common ancestor of all land plants has already entered into a partnership with the arbuscular mycorrhizal fungus 450 million years ago,” the scientist writes.
Source: CNRS, Technical article: Science, doi: 10.1126 / science.abg0929