Two essential genes have been identified for plants that colonized the Earth 470 million years ago

Scientists think it’s possible that the two genes, PEN1 and SYP122, paved the way for all kinds of terrestrial plant life.

Researchers have shed new light on how plant life establishes itself on Earth

Researchers from the University of Copenhagen shed new light on how plant life is established on the surface of our planet. In particular, they showed that two genes are necessary for land plants to protect themselves from fungal attacks – a defense mechanism dating back 470 million years. These defenses may have paved the way for all kinds of terrestrial plant life.

Mads Eggert Nielsen, a biologist at the University of Copenhagen.

Plants evolved from aquatic algae to the ability to survive on Earth about half a billion years ago, laying the foundation for life on Earth. Mushrooms were one of the obstacles that made this dramatic transformation so difficult:

“It is estimated that 100 million years ago, fungi slithered across the Earth’s surface in search of food, most likely finding it in dead algae washed up in the sea. So if you, as a new plant, were to establish yourself on the ground, “The first thing I encountered was a type of fungus that was going to eat you, I needed some kind of defense mechanism,” says Mads-Egert Nielsen, a biologist in the Department of Plants and Scientific Ecology from the University of Copenhagen.

According to Mads Eggert Nielsen and fellow researchers from the Department of Plant and Environmental Sciences and the University of Paris-Sclay, the core of this defense mechanism can be reduced to two genes, PEN1 and SYP122. Together, they help form a type of plant that prevents the invasion of fungi and fungi-like organisms.

We discovered that if we destroy these two genes in our model plant, Arabidopsis (Arabidopsis), we open the door to entry for pathogenic fungi. We have found that they are essential for the formation of that cell wall-like plug that protects against fungi. Interestingly, it appears to be a universal defense mechanism present in all land plants,” says Mads Eggert Nielsen, lead author of the study, which was published in the journal Science. eLife.

It comes from a plant that is 470 million years old

The research team tested the same function in the liverwort, a direct descendant of one of the oldest land plants on Earth. By taking the two matching genes in the liverwort and inserting them into the Arabids plant, the researchers examined whether they could determine the same effect. The answer was yes.

Plant Model Thale Cress

Experiments with the model plant Arabidopsis (Arabidopsis) Credit: Mads Eggert Nielsen

“Although the two plant families to which Arabidopsis and liverwort belonged evolved in divergent directions 450 million years ago, they continued to share genetic functions. We believe that this family of genes arose with the sole purpose of managing this defense mechanism, and thus was one of the bases on which plants rested to establish themselves on Earth,” explains Mads Eggert Nielsen.

The coexistence of plants and fungi

While fungi were an obstacle to plants in their transition from the marine algae stage to land plants, they were also a prerequisite. Once the plants were able to survive the attacks of the fungi seeking to eat them on Earth, the next problem they faced was finding the nutrients, says Mads Eggert Nielsen:

Dissolved nutrients such as phosphorous and nitrogen are readily available to plants in aquatic environments. But 500 million years ago, the Earth as we know it today didn’t exist, just rocks. In addition, it is very difficult for plants to obtain the nutrients found in rocks. But not for mushrooms. On the other hand, mushrooms cannot produce carbohydrates, which is why they are consumed by plants. Here it is believed that a symbiotic relationship between plants and fungi arose, which later became the basis for the explosion of terrestrial plant life during this period.

The defensive structures that form in the plant do not kill the plant or the fungus, they simply prevent the fungus from invading.

“Because the fungus can only partially penetrate the plant, we believe the tipping point occurs where both the plant and the fungus have something to gain. Therefore, it was useful to maintain the relationship such as the theory that plants tamed fungi to colonize our land, but we provide forage that supports this idea,” says Mads Eggert Nielsen.

Can be applied in agriculture

The new findings add an important piece to the puzzle of plant evolutionary history. More importantly, they can be used to make crops more resistant to fungal attack, which is a big problem for farmers.

“If all plants defend themselves in the same way, that should mean that disease-causing microorganisms – such as powdery mildew, striped rust and potato mold – have found a way to sneak inside.” or extinguishing or escaping from the defenses of its host. We want to know how they do it. We will then try to transfer the defensive components of the resistant plants to the plants that become ill, thus achieving resistance,” explains Mads Eggert Nielsen.

Mads Eggert Nielsen is participating in a research project in the Department of Plant and Environmental Sciences led by Hans Thordahl Christensen and supported by the Novo Nordisk Foundation that aims to make crops more resilient by identifying plant defense mechanisms that attempt disease-causing microorganisms. to shut down.

Additional facts

Researchers have long speculated that the genes PEN1 and SYP122 perform a certain function in relation to the transition of plants from their aquatic phase as algae to terrestrial plants, but there has been no concrete evidence as to whether they are indeed a prerequisite for plants. defensive capabilities.

Previous studies have shown that by eliminating the PEN1 gene, plants lose their ability to defend against powdery mildew. However, when the closely related gene, SYP122, is eliminated, nothing happens. The new research results show that the two genes together represent an important key in the plant’s defense mechanism.

Reference: “SYP12 Plant Syntaxins mediate evolutionarily conserved general immunity against filamentous pathogens” by Hector M Rubiato, Mingqi Liu, Richard J O’Connell and Mads E. Nielsen, 4 February 2022, eLife.
DOI: 10.7554 / eLife.73487