Researchers shed new light on how plant life established itself on Earth’s surface
Researchers from the University of Copenhagen have shed new light on how plant life established itself on the surface of our planet. In particular, they demonstrated that two genes are crucial for land plants to protect themselves against fungal attacks – a defense mechanism that dates back 470 million years. These defenses probably paved the way for all terrestrial plant life.
Plants evolved from aquatic algae to be able to survive on land about half a billion years ago, laying the foundations for life on earth. Mushrooms were one of the obstacles that made this dramatic transition so difficult:
“It is estimated that 100 million years ago, fungi slithered across the Earth’s surface in search of food and most likely found it in dead algae washed out to sea. So if you , as a new plant, were going to establish yourself on earth and the first thing you encountered was a fungus that would eat you, you needed some sort of defense mechanism,” says Mads Eggert Nielsen, a biologist in the Department of Science Plants and Environments from the University of Copenhagen.
According to Mads Eggert Nielsen and his fellow researchers from the Department of Plant and Environmental Sciences and the University of Paris-Saclay, the essence of this defense mechanism can be reduced to two genes, PEN1 and SYP122. Together they help form a sort of plug in plants that blocks the invasion of fungi and fungus-like organisms.
“We have discovered that if we destroy these two genes in our model plant, Arabidopsis (Arabidopsis), we open the door to the entry of pathogenic fungi. We’ve found that they’re essential for forming that 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, published in the journal eLife.
Originating from a 470 million year old plant
The research team tested the same function in liverwort, a direct descendant of one of Earth’s earliest land plants. By taking the two corresponding genes in the liverwort and inserting them into the Arabid, the researchers examined whether they could identify the same effect. The answer was yes.
“Even though 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 family of genes emerged for the sole purpose of managing this defense mechanism and was therefore one of the bases for plants to establish themselves on earth,” says Mads Eggert Nielsen.
A symbiosis between plants and fungi
While fungi were an obstacle for plants in their transition from a marine algal stage to becoming land plants, they were also a prerequisite. As soon as plants were able to survive attacks by fungi seeking to eat them on land, the next problem they faced was finding nutrients, says Mads Eggert Nielsen:
“Dissolved nutrients like phosphorus and nitrogen are readily available to plants in aquatic environments. But 500 million years ago, the ground as we know it today did not exist, only rocks. Additionally, rock-bound nutrients are extremely difficult for plants to obtain. But not for mushrooms. On the other hand, mushrooms cannot produce carbohydrates, which is why they consume plants. It was 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.
The defense structures that form in a plant do not kill the plant or the fungus, they simply prevent a fungus from invading.
“Since a fungus can only partially enter a plant, we believe a tipping point occurs where both the plant and the fungus have something to gain. Therefore, it has been beneficial to keep the relationship as is. The theory that plants tamed fungi to colonize the earth is not ours, but we provide fodder 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 could 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 disease-causing microorganisms – such as powdery mildew, stripe rust and potato mold – have found a way to sneak in. “, extinguish or escape the defenses of their 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 the plants that become diseased, and thus achieve resistance”, explains 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 aims to make crops more resilient by identifying plant defense mechanisms that micro- disease-causing organisms try to shut down.
Researchers have long speculated that the PEN1 and SYP122 genes served a particular function with respect to the transition of plants from their aquatic stage as algae to terrestrial plants, but there has been no concrete evidence as to whether if they were actually a prerequisite for plants. ‘ defensive abilities.
Previous studies have shown that by knocking out the PEN1 gene, plants lose their ability to defend against powdery mildew fungi. However, upon knocking out the closely related gene, SYP122, nothing happens. The new research results demonstrate that together the two genes are 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, Mengqi Liu, Richard J O’Connell and Mads E Nielsen, 4 February 2022, eLife.