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Two Genes Crucial to Plants That Colonized Earth 470 Million Ago Have Been Identified

Earth DNA Genetics
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World DNA Genetics

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

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

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

Mads Eggert Nielsen

Mads Eggert Nielsen, biologist from the University of Copenhagen.

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

“It’s estimated that 100 million years ago, fungi slithered to the Earth’s surface in search of food and most likely found it in dead algae that had been washed out of the sea. So, if you were to establish yourself on land as a new plant and the first thing you encounter was a fungus that would eat you, you might have some kind of defense mechanism. you needed it,” says biologist Mads Eggert Nielsen, Department of Plant and Environmental Sciences at the University of Copenhagen.

The essence of this defense mechanism can be narrowed down to two genes, PEN1 and SYP122, according to Mads Eggert Nielsen and colleagues from the Department of Plant and Environmental Sciences and the University of Paris-Saclay. Together, they help form a kind of plug in plants that inhibits the invasion of fungi and fungus-like organisms.

“We learned that if we knock out these two genes in our Thale cress model (Arabidopsis), we open the door for pathogenic fungi to penetrate. We found that they are necessary to form this cell wall-like plug that defends against fungi. Interestingly, it appears to be a universal defense mechanism found in all terrestrial plants. ”says Mads Eggert Nielsen, senior author of the study published in the journal Nature. e-life.

Originated from a 470-million-year-old plant

The research team tested the same function in liverwort, a direct descendant of one of Earth’s first land plants. The researchers examined whether they could describe the same effect by taking two corresponding genes in liverwort and adding them to cress. The answer was yes.

Model Plant Thale Cress

Experiments on a cress plant (Arabidopsis) model Credits: Mads Eggert Nielsen

Although the two plant families Arabidopsis and liverwort belong to evolved in different directions 450 million years ago, they continue to share genetic functions. “We believe that this gene family arose with the unique purpose of governing this defense mechanism and is therefore one of the foundations for plants to establish themselves on land,” says Mads Eggert Nielsen.

A symbiosis between plants and fungi

While fungi were a barrier to the transition of plants from the algae marine stage to land plants, they were also a prerequisite. Mads Eggert Nielsen explains that as soon as plants recover from the onslaught of fungi trying to eat themselves on land, the next problem they will face is finding food:

“Dissolved nutrients such as phosphorus and nitrogen are easily accessible by plants in aquatic environments. But 500 million years ago, there was no soil as we know it today, only rocks. And the nutrients attached to the rocks are extremely difficult for plants. But not for mushrooms. Fungi, on the other hand, cannot produce carbohydrates – so they consume plants. It is here that a symbiotic relationship between plants and fungi is believed to have arisen, which later became the basis for the explosion of terrestrial plant life during this period. ”

Defense structures formed in a plant do not kill either the plant or the fungus, they only prevent the invasion of a fungus.

“Because a fungus can only partially enter a plant, we believe a tipping point has arisen where both the plant and the fungus have something to gain. So it has been an advantage to keep the relationship intact. The theory is not ours that plants domesticated fungi to colonize the soil, but this is not ours. We provide the bait that supports the idea,” says Mads Eggert Nielsen.

Applicable in agriculture

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

“If all plants protect themselves the same way, it must mean that microorganisms that can cause diseases such as powdery mildew, yellow rust, and potato mold have found a way to sneak in, shut down or avoid their defenses from suitable host plants. We want to learn how they do it. Next, from resistant plants.” We will try to transfer the defense components to the plants that have become diseased and thus acquire 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, which focuses on making plants more resilient by identifying the defense mechanisms of pathogenic microorganisms in plants. close.

Additional information

Researchers have long assumed that the PEN1 and SYP122 genes serve a specific function in the transition of plants from their aquatic stages as algae to land plants, but no concrete evidence has been found as to whether they are truly a prerequisite for plants. ‘defensive abilities.

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

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

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