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Mushrooms conquering the emerged lands

Mushrooms have helped plants conquer land


Networks of underground fungi have been an essential partner of plants since their conquest of land 450 million years ago, confirmed a scientific study published recently.


An international team of researchers, led by those from the Plant Science Research Laboratory (LRSV) at Toulouse-III, have found the missing link in a theory dating back to the 1980s.

She posits that the ancestor of all existing land plants, presumably a freshwater algae that emerged from the waters around 450 million years ago, lived in symbiosis with tiny fungi to grow on Earth. .


Today, about 80% of terrestrial plants use this symbiosis, in which the underground fungus "is really an extension of the plant", explains to AFP Pierre-Marc Delaux. CNRS researcher at LRSV, he is the main co-author of the study published in Science (in English) last week and signed by his colleague and postdoctoral fellow Mélanie Rich.

The mycelium of the mushroom, its vegetative apparatus, is made up of an innumerable quantity of tiny white filaments, which extend in a network into the subsoil. Its microscopic extremities, intimately linked to the roots of the plant, mainly provide it with water, nitrogen and phosphates. In exchange, the plant supplies the fungus with lipids, a fat essential for its development.


"If one of the two partners stops feeding the other, the exchanges stop in both directions", and everyone suffers, explains Mr. Delaux: fungi, which depend "100% on the plant for their development”, as well as the plant, which can manage in a rich ecosystem, but “will suffer much more in a very impoverished soil”.


The consequences of a stoppage of the symbiosis go far beyond that, because the mycelium of the fungus spreads like a sprawling hair.

“Fungi are connected to hundreds, even thousands of plants at the same time,” says Delaux, who reports “pretty convincing work” on the role they play in distributing resources in this ecosystem.


The researchers' study demonstrated that the same "symbiotic" gene, known to play an essential role in the transfer of lipids from the plant to the fungus, was at work in the two main branches of terrestrial plants. therefore conclude "that their common ancestor who lived 450 million years ago also had these genes", according to the researcher.


The mechanism was already well identified for vascular plants, with stems and roots. It has been found in non-vascular plants, such as mosses, called bryophytes, that “another great lineage of land plants”.

Scientists have confirmed the role of the famous gene by depriving a "mutant" of a moss, Marchantia paleacea. With the direct consequence of the failure of the symbiosis and the cessation of the development of the fungus.


To achieve its goals, the LRSV team worked with a host of European researchers, from the Universities of Cologne, Zurich, Leiden and Cambridge, among others, and Japanese, from the University of Sendai.


LRSV research is now moving towards another kind of symbiosis, explains Mélanie Rich. That which is exercised between plants and “nitrogen-fixing bacteria, which make it possible to recover atmospheric nitrogen and fertilize the plants with which they cohabit”.


This symbiosis exists in legumes such as lentils. The researchers hope to “recreate it with plants of agronomic interest such as wheat, corn, rice”, and to “contribute to the transfer of intensive agriculture which impoverishes the soil towards more sustainable agriculture”. adds the researcher.

Because mastering this symbiosis would make it possible to limit the massive use of nitrogenous fertilizers in rich countries, and to compensate for their absence in the poorer countries of Africa and South-East Asia.

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