Two genes that are essential for plants that colonize the earth 470 million years ago have been identified

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

Scientists shed new light on how plant life was established on the earth’s surface

Researchers from the University of Copenhagen have shed new light on how plant life was established on the surface of our planet. They specifically demonstrated that two genes are essential for land plants to protect themselves against fungal attacks – a defense mechanism that dates back 470 million years. These defenses most likely paved the way for all terrestrial plant life.

Mads Eggert Nielsen

Mads Eggert Nielsen, biologist at the University of Copenhagen.

Plants evolved from aquatic algae to be able to survive on land about half a billion years ago, and laid 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 above the earth’s surface in search of food and most likely found it in dead algae that were washed up from the sea. So if you as a new plant were to establish yourself on land, and the first thing you encountered was a fungus that wanted to eat you, you needed a kind of defense mechanism, says Mads Eggert Nielsen, biologist at the University of Copenhagen’s Department of Plant and Environmental Sciences.

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

“We found that if we destroy these two genes in our model plant thale watercress (Arabidopsis), we open the door for pathogenic fungi to penetrate. We found that they are essential for the formation of this cell wall-like plug that defends against fungi. Interesting enough, it seems to be a universal defense mechanism found in all land plants, says Mads Eggert Nielsen, senior author of the study, which is published in the journal. eLife.

Originated in a 470 million year old facility

The research team has tested the same function in liver must, a direct descendant of one of the earth’s very first land plants. By taking the two corresponding genes in the liver puree and inserting them into the watercress, the researchers examined whether they could identify the same effect. The answer was yes.

Model Plant Thale Cress

Experiments on the model plant thalse 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 originated with the unique purpose of managing this defense mechanism and has thus been one of the basis for plants to have established themselves on land, says Mads Eggert Nielsen.

A symbiosis between plants and fungi

While fungi were an obstacle for plants in their transition from an algae stage to becoming land plants – they were also a prerequisite. As soon as plants could survive attacks from fungi that would eat them on land, the next problem they faced was finding nutrients, explains Mads Eggert Nielsen:

“Dissolved nutrients such as phosphorus and nitrogen are readily available to plants in aquatic environments. But 500 million years ago, soil did not exist as we know it today – only rocks. And nutrients bound in rocks are extremely difficult for plants to obtain. But not for fungi.On the other hand, fungi can not produce carbohydrates – that is why they eat plants.This is where a symbiotic relationship between plants and fungi is believed to have arisen, which then became the basis for the explosion of terrestrial plant life during this period. »

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

“Since a fungus can only get partial access to a plant, we believe that there is a tipping point where both plant and fungus have something to gain. Therefore, it has been an advantage to maintain the relationship as it is. The theory that plants tame mushrooms to colonize land is not ours, but we provide feed that supports this idea, says Mads Eggert Nielsen.

Can be used in agriculture

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

“If all plants defend themselves in the same way, it must mean that the microorganisms that are capable of causing diseases – such as mold, yellow rust and potato fungi – have found a way to sneak in, turn off or escape their defenses. respective host plants. We want to find out how they do it. We will then try to transfer defensive components from resistant plants to the plants that become ill, and thus achieve resistance, says Mads Eggert Nielsen.

Mads Eggert Nielsen is involved in a research project at the Department of Plant and Environmental Sciences led by Hans Thordal-Christensen and supported by the Novo Nordisk Foundation, which focuses on making crops more resistant by identifying the defense mechanisms in plants that pathogenic microorganisms try to turn off.

Additional facts

Researchers have long believed that the genes PEN1 and SYP122 have served a special function in relation to the transition of plants from their water stage as algae to terrestrial plants, but there has been no concrete evidence as to whether they were in fact a prerequisite for the plants. ‘defensive abilities.

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

Reference: “Plant SYP12 Syntaxes Convey an Evolutionary Preserved General Immunity to Filamentous Pathogens” by Hector M Rubiato, Mengqi Liu, Richard J O’Connell and Mads E Nielsen, February 4, 2022, eLife.
DOI: 10.7554 / eLife.73487