Life on Earth is made up of billions of kilometers of thread. Which are woven by fungi. If we know porcini mushrooms well, we have little doubt that 90% of terrestrial plants belong to a little known class of glomeromycetes. These fine fibers called hypohe, less than 500 microns in diameter, provide essential organic matter to plants and in turn receive lipids that they are unable to produce. It is believed that there are thousands of species, but research has emerged against the difficulty of seeing these organisms made up of a single cell with thousands of nuclei. “They cannot really be cultivated alone in the laboratory because they require their connection to plants.“, Specifies CNRS researcher Pierre-Marc Delaux at the University of Toulouse III. This relationship is strong and longstanding. Science, The Toulouse team has just given evidence that glomeromycetes played a major role in conquering land by plants 750 million years ago.
The growth of plants on the way out of the sea. Bryophytes are the closest form of early land plants. Copyright Deluxe / Rich
His role was certainly questionable. In the 1980s, exploitation of the fossil deposits of Rhynie chaille (Scotland) showed the presence of these fibers inside the cells of fossil plants 407 million years old. “High-resolution microscopy revealed structures that resemble the fungus’s arbuscules but one can only see very closely the presence that can be seen in plant roots today”, Continues Pierre-Marc Delaux. In the mid-2010s, research on the genomes of flowering plants (angiosperms), conifers (gymnosperms), and plants lacking sap-delivery vessel systems, bryophytes (moss, liverworts), showed that genes involved in this symbiosis in angiosperms Are present in all plants. . Therefore this faculty of symbiosis seemed very old: it was already related to the ancestor of all plants.
The relationship between plants and fungi has changed little over the last 450 million years
This does not mean that the essential role of symbiosis in the evolutionary success of plants is evidenced. “We then used a model bryophyte, the Merchantia palacea, to make the mutants, Description Melanie Rich, co-author of the article Science. Using the purity of CRISPR / Cas9 “molecular scissors”, we inactivated one of the symbiotic genes and thus inhibited the exchange of lipids with fungi.“. Plants and fungi no longer interact, experience has shown the essential role of these exchanges. And if plants are able to survive without fungi, the reverse is not true. “Perhaps the most incredible is that bryophytes, flowering plants, conifers have a lot of diversity and are nothing like plants from 400 million years ago and yet symbiosis is very similar” Melanie Rich is surprised. Therefore, the hypothesis of mushroom’s essential role in the conquest of the land has now been confirmed.
There are still many unanswered science questions on this subject. For example, the biodiversity of glomeromycetes is still poorly understood, although they are essential for plants cultivated by humans, much like the harmful effects of chemical inputs used by traditional agriculture on these precious adjuvants. Less is studied. And it also remains to be better understood how the fungus intervened to allow green algae to take root in the soil. Algae today do not contain symbiotic fungi and when flowering plants return to the sea such as Posidonia and Zosteria, they lose their symbiotic capacity. Evidence that life in water rests on threads …