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

Earth DNA Genetics
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Earth DNA Genetics

Scientists believe that the two genes, PEN1 and SYP122, likely paved the way for all terrestrial plant life.

Researchers shed new light on how plant life became established on Earth’s surface

Researchers of the University of Copenhagen have shed new light on how plant life became established on the surface of our planet. They specifically showed that two genes are crucial for terrestrial plants to protect themselves against fungal attack, a defense mechanism that dates back 470 million years. These defenses probably paved the way for all terrestrial plant life.

Mads Eggert Nielsen

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

Plants evolved from aquatic algae to being able to survive on land approximately half a billion years ago, laying the foundation for life on land. Mushrooms were one of the obstacles that made this dramatic transition so difficult:

“It is estimated that 100 million years earlier, fungi crawled across the Earth’s surface in search of food and most likely found it on dead algae washed up by the sea. So if you, as a new plant, were going to establish yourself on land, and the first thing you encountered was a fungus that was going to eat you, you needed some kind of defense mechanism,” says Mads Eggert Nielsen, a biologist in the Department of Plant Sciences and Environmental at the University of Copenhagen.

According to Mads Eggert Nielsen and his fellow researchers at the Department of Plant and Environmental Sciences and the University of Paris-Saclay, the essence of this defense mechanism can be boiled down to two genes, PEN1 and SYP122. Together, they help form a kind of plug in plants that blocks the invasion of fungi and fungus-like organisms.

“We found that if we knock out these two genes in our model plant thale cress (Arabidopsis), we open the door for fungal pathogens to enter. We found that they are essential for forming this cell wall-like plug that defends against fungi. Interestingly, it appears to be a universal defense mechanism found in all land plants,” says Mads Eggert Nielsen, lead author of the study, which is published in the journal eLife.

It originated from a 470 million year old plant.

The research team has tested the same function in liverwort, a direct descendant of one of the first land plants on Earth. By taking the two corresponding genes in liverwort and inserting them into thale cress, the researchers examined whether they could identify the same effect. The answer was yes.

Thale Watercress Model Plant

Experiments on the model plant thale cress (Arabidopsis) Credit: Mads Eggert Nielsen

“Although the two plant families to which Arabidopsis and liverwort belong evolved in divergent directions 450 million years ago, they continue to share genetic functions. We believe that this gene family arose for the sole purpose of managing this defense mechanism, and thus has been one of the foundations for plants to establish themselves on land,” says Mads Eggert Nielsen.

A symbiosis between plants and fungi

While the fungi represented an obstacle for plants in their transition from a seaweed stage to becoming land plants, they were also a prerequisite. As soon as plants were able to survive attacks from fungi seeking to eat them in the soil, the next problem they faced was finding nutrients, explains Mads Eggert Nielsen:

“Dissolved nutrients like phosphorus and nitrogen are easily accessible to plants in aquatic environments. But 500 million years ago, soil as we know it did not exist today, only rocks. And, rock-bound nutrients are extremely difficult for plants to obtain. But not for mushrooms. On the other hand, fungi cannot produce carbohydrates, which is why they consume plants. This is where a symbiotic relationship between plants and fungi is thought to have emerged, which then became the basis for the explosion of terrestrial plant life during this period.”

The defense structures that form on a plant do not kill either the plant or the fungus, they simply prevent the fungus from invading.

“Since a fungus can only partially enter a plant, we think a tipping point arises where both the plant and the fungus have something to gain. Therefore, it has been an advantage to keep the relationship as it is. The theory that plants domesticated fungi to colonize land is not ours, but we are providing fodder that supports this idea,” says Mads Eggert Nielsen.

It can be applied in agriculture.

The new results add an important piece to the puzzle of the evolutionary history of plants. More importantly, they could be used to make crops more resistant to fungal attacks, which is a major problem for farmers.

“If all plants defend themselves in the same way, it must mean that disease-causing microorganisms – such as powdery mildew, yellow rust and potato mold – have found a way to sneak in, shut down or evade the defenses of their plants.” respective host plants. We want to know how they do it. We will then try to transfer the defensive components of the resistant plants to those plants that get sick and thus achieve resistance,” says Mads Eggert Nielsen.

Mads Eggert Nielsen is involved in a research project in the Department of Plant and Environmental Sciences led by Hans Thordal-Christensen and supported by the Novo Nordisk Foundation that focuses on making crops more resilient by identifying the defense mechanisms in plants that pathogenic microorganisms are trying to shut down.

Additional data

Researchers have long assumed that the PEN1 and SYP122 genes have served a special role in transitioning plants from their aquatic stage as algae to terrestrial plants, but there has been no concrete evidence that they were actually a prerequisite for the plants. ‘defensive skills.

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

Reference: “Plant SYP12 Syntaxins Mediate an Evolutionarily Conserved General Immunity Against Filamentous Pathogens” by Hector M Rubiato, Mengqi Liu, Richard J O’Connell, and Mads E Nielsen, Feb 4, 2022, eLife.
DOI: 10.7554/eLife.73487

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