La bryophite Marchantia paleacea

Plants came out of the sea thanks to the fungi

Life on Earth is made up of billions of kilometers of filaments. Those woven with fungi. If we knew all too well porcini mushrooms, we suspect that less than 90% of terrestrial plants are associated with an unknown class, glomeruli. These tiny filaments, called filaments with a diameter of less than 500 microns, provide plants with the organic matter they need and in return receive fats that they cannot produce. Presumably there are thousands of species, but research has struggled to monitor these single-cell organisms with thousands of nuclei. “It cannot really be grown on its own in the laboratory because it needs to be related to plants.“This relationship is strong and… ancient. ScienceThen, the Toulouse team has just provided evidence that glomeruli played a major role in plants invading Earth 450 million years ago.

Plants develop when the seas are out. Bryophytes are the earliest forms of the first land plants. Copyright Delaux / Rich

Their role was definitely questionable. In the 1980s, exploiting fossil deposits Rhynie’s chaille (Scotland) He showed the presence of these filaments inside fossilized plant cells dating back 407 million years. “High-resolution microscopy revealed structures similar to tree mushrooms but one could only see an appearance very close to that seen in plant roots today.”Pierre Marc Delaux continues. In mid-2010, research on the genomes of flowering plants (angiosperms), conifers (gymnosperms), plants lacking vascular systems for sap distribution, and algal plants (algae and hepatoprotectors) showed that the genes involved in this symbiosis in angiosperms are present in all plants. . So this queen of symbiosis looked very old: it really belongs to the ancestor of all plants.

The relationship between plants and fungi has changed little over the past 450 million years

This does not mean that evidence has been provided of the essential role of symbiosis in the evolutionary success of plants. “Then we used an algal plant model, Marchantia paleacea, to generate mutations, Details Melanie Rich, co-author of an article by Science. Using the resolution of CRISPR / Cas9 “molecular scissors”, we inactivated a symbiotic gene and thus observed a cessation of lipid exchange with fungi.“The plant and the fungus no longer interact, and experience has shown the fundamental role of these exchanges. And if plants are able to survive without the fungi, then the opposite is not true. “Perhaps the most impressive thing is that algae, flowering plants, and conifers have varied so much and do not look like plants of 400 million years ago, yet the coexistence is still very similar.” Melanie Rich was surprised. Therefore, the hypothesis of the essential role of fungi in invading Earth is now confirmed.

There are still many unanswered scientific questions on this topic. For example, the biological diversity of glomeruli is still poorly understood, although it is still essential for plants grown by humans, just as the harmful effects of chemical inputs used in conventional agriculture on these valuable auxiliaries have not been studied much. It also remains to understand better how fungi intervene to allow green algae to take root in the soil. Today’s algae do not contain symbiotic fungi and when flowering plants like Posidonia and Zoosteria return to the sea, they lose their symbiotic capabilities. Proving if there is ever life outside of water sticks to the strings …

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