Alliance between plants and fungi led to living on land

Plants may have colonised land because of an alliance with fungi, according to a study published in Science.

Plants began life as aquatic species and started to move onto land around 450 million years ago. In the 1980s, a fossil study led to a hypothesis that they were able to adapt to the arid, above-water environment because of a partnership with fungi.

Now, researchers from the French National Centre for Scientific Research and the Université de Toulouse III – Paul Sabatier, France, validated the 40-year-old hypothesis, using a succulent plant called Marchantia paleacea.

There are two major plant types. The first are vascular plants, which are the “typical” plants with stems and roots (a vascular system). The other non-vascular plants are called bryophytes, including things like mosses and liverwort. M. paleacea is one of the latter.

Family tree of evolution with fungi. Circles on the left: the fungus is stained blue in a truncated alfalfa root (top) or a thallus of M. paleacea (bottom). Right-hand circles: stubby alfalfa (top), M. paleacea (bottom). Credit: Aurélie Le Ru/Mélanie Rich/Pierre-Marc Delaux.

The team identified a gene in M. paleacea that helped it maintain a symbiotic relationship with fungi, by allowing it to share lipids (fats) with its fungal friend.

The researchers then used CRISPR – a gene editing technique – to modify the gene and found that the bryophyte could no longer carry on its symbiotic relationship with the fungus.

This had been previously demonstrated in vascular plants, but because both of the completely different plant groups reacted the same to the edited gene, it means they both received the trait from an ancient ancestor.

Based on their family tree, the ancestor that evolved this trait would likely have been one of the plants that moved out of the water, which means the relationship between plants and fungi is very old indeed.

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