UThe international team of researchers led by the Laboratory for Research in Plant Sciences (LRSV) of Toulouse-III have found the missing link in a theory of the 1980s. It assumes that the ancestors of all terrestrial plants existing, possibly from a freshwater algae and originating from water about 450 million years ago, lived in symbiosis with small fungi to flourish on Earth.

Today, about 80% of land plants use this symbiosis, with underground fungi “actually being an extension of the plant,” Pierre-Marc Delaux told AFP. A CNRS researcher at LRSV, she is the lead co-author of the study published in Science last week and signed by her colleague and post-doctoral fellow Melanie Rich. The mycelium of the fungus, its botanical device, contains a myriad of small white fibers, which network in the sub-soil. Its microscopic ends are intimately connected to the roots of the plant, giving it mainly water, nitrogen, and phosphate. In turn, the plant provides lipids to the fungus, which is the fat required for its growth.

Spread hair

“If one of the two partners stops feeding each other, the exchange stops in both directions”, and everyone suffers, explains Mr. Delaux: the fungus, which “100s on the plant for its growth % “Depends, as well as plants, which can survive in a rich ecosystem but” will suffer too much in very poor soils “.

The consequences of stopping symbiosis go much further, as the mycelium of the fungus spreads like a hair that has spread. “Fungi are linked to thousands, if not hundreds, of thousands of plants at the same time,” says Dalloux, who reports “quite solid work” on the role they play in allocating resources to this ecosystem.

Researchers’ studies showed that the same “symbiotic” gene, known to play an essential role in the transfer of lipids from plants to fungi, was operating in two major branches of terrestrial plants. We can therefore conclude that “their common ancestor who lived 450 million years ago also had these genes”, according to the researcher. The mechanism for vascular plants with stems and roots was already well recognized. It has been found in non-vascular plants, such as mosses, called bryophytes, that “another great line of land plants”.

Mutant mousse

Scientists have confirmed the role of the famous gene by denying it a “mutant” of a foam, Merchantia palacea. With the direct consequence of concomitant failure and inhibiting the growth of fungi. To achieve their goals, the LRSV team worked with several European researchers from the Universities of Cologne, Zurich, Leiden and Cambridge, and the Japanese at Sendai University.

Melanie Rich points out that LRSV research is now moving towards a different kind of symbiosis. The one that is planted between plants and “nitrogen fixing bacteria, which make it possible to recover atmospheric nitrogen and fertilize the plants with which they coexist”.

It is present in beans like sahajivan dal. The researchers hope to “recreate it with plants of agricultural interest such as wheat, corn, rice”, and to “contribute to the transfer of intensive agriculture that leads the soil to more sustainable agriculture”, the researchers it is said. Because mastering this symbiosis will limit the large-scale use of nitrogen fertilizers in rich countries, and compensate for their absence in poor countries, Africa and Southeast Asia.