Coping with phyto-mushrooms leaves the primeval shore with friends

“Friendship” apparently formed the basis of the green revolution on our planet: researchers provided new evidence that plant colonization in the country was possible about 450 million years ago through a symbiotic relationship with fungi. They were able to demonstrate that even simple liverworts – considered live fossils – offer fats to their fungal partners as “commercial goods” – similar to a highly evolved plant species. However, in the case of algae, there is no corresponding lipid biosynthesis. With this in mind, the scientists concluded that this system dates back to the time when the first plants turned the country green with the support of their mushroom partners.

Most plant species today have loyal partners: they enter into an intimate relationship with the species of fungi that live in the soil, through which they can obtain additional nutrients and water from the soil. In this so-called fungal root symbiosis, the partners exchange nutrients via a connection between the fungal network circulating in the soil and the roots of the plant. In the most common form, the ‘trade’ takes place through a complex structure within the roots: the fungus penetrates through it and forms a tree-like structure (arbuscle) in some cells with the plant. Then the feeders are transported over the large surface of this structure. The fungus gives the plant water and above all the nutrient phosphate that it absorbs from the soil. In return, the plant supplies him with materials rich in energy. Studies have shown that in addition to sugar molecules, fats are also involved.

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Pioneer recipe for success?

As early as the 1980s, plant fossil studies showed that the mycorrhizal symbiosis is archaic. Doubts arose that the partnership may have enabled the plants to go ashore about 450 million years ago: in their harsh new habitat, the fungi may have been able to provide the pioneer plants with water and nutrients in a decisive way. The current study by researchers led by Melanie Rich of the University of Toulouse supports this assumption with genetic and molecular biological evidence.

They rely on the results of long-term research into the genetic makeup that enables plants to enter into a complex relationship with fungi. So far, the focus has been on modern vascular plants (tracheophytes) such as beans, potatoes and the like. But Rich and her colleagues have now devoted themselves to plants that still resemble the pioneers of the plant-based beach vacation: mosses. It is thought to have evolved from green algae in the intertidal zone 450 million years ago.

It is known that these primitive plants can also form partnerships with fungi – but the genetic and molecular basis of symbiosis of fungi and algae has yet to be explored. As part of their study, researchers have now considered Marchantia paleacea as a model that forms a tree root symbiosis with fungi. Using both genetic and molecular biological methods, the team investigated the genetic factors and processes that become active in plants as tree-like exchange structures arise in their cells and come into effect.

The old principle

They were able to prove that fats are also transferred from the plant to the fungi in the liverwort. The researchers were able to demonstrate that this is the same basic principle of lipid transport as in modern vascular plants. As with these, the process is also a prerequisite for algae to be able to form symbiosis. The researchers were able to show this on transgenic algal blooms, in which they switched off the genetic make-up necessary for lipid transport. Studies have shown that these young plants can no longer establish a partnership with fungi.

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The researchers were also able to demonstrate that the lipid biosynthesis system for vascular plants and algae needed for coexistence is not present in the aquatic algae from which green Earth pioneers were once thought to have originated. In these results, you see a clear indication that the evolution of fungal symbiosis was at the beginning of the evolutionary history of the Earth’s flora and may represent a prerequisite for the successful invasion of the new habitat. The scientists wrote: “Our results indicate that the common ancestor of all the plants of the Earth actually entered into a partnership with the spiny root fungi 450 million years ago.”

Source: CNRS, Technical Article: Science, doi: 10.1126 / science.abg0929

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