They are squashed and broken by weather events and human activities. Larvae munch the leaves, and they fall prey to disease. Plants are indeed exposed to many trials and tribulations, but they are also very resilient, with an impressive ability to detect and repair damage. In the lab at the Swedish University of Agricultural Sciences (SLU) in Uppsala, Stael is studying the molecular strategies behind the response of plants to stress and damage.

“Plants are rooted in the ground – they can’t run away and hide. This means they have to be highly resilient and aware of changes in their environment, and cope with whatever befalls them. Just a few seconds after a plant is damaged it is aware that something has happened and reacts. But we should be careful not to compare plant responses with human feelings and experience of for example pain,” says Stael.

As a Wallenberg Academy Fellow, he is studying a group of proteins – enzymes – called proteases. Their task is to cleave other proteins, thereby altering their function. Proteases are found in all living organisms, including humans and other animals. Stael has demonstrated that a protease called metacaspase plays a key role in damage response in plants, findings the research team is now building on.

The research has the potential to contribute to better plant protection for sustainable agriculture and forestry, and higher crop yields.

“Just a few seconds after a plant is damaged it is aware that something has happened and reacts accordingly.”

Stael elaborates:
“I always have ideas in the back of my mind about how my research can be put to use in society. My team and I are trying to use our knowledge about what happens when plants are damaged to create agricultural pesticides that better target pests and are not harmful to beneficial insects. It would be great if in five years’ time we have a first generation of these modified pesticides.”

Immune-like response

Stael studied biology and biotechnology at the University of Ghent in Belgium, his home country. Work on his master’s in plant biology and plant stress acclimatization at Turku University in Finland marked the beginning of his research career. In the fall of 2022 Stael left the VIB-UGent Center for Plant Systems Biology in Belgium to join SLU, where he now has his own research team.

Plants have no immune system or blood that can coagulate. Their response to damage is instead based on molecular signal mechanisms that act both locally in damaged cells and more peripherally in other parts of the plant.

In previous studies of metacaspases – a group of proteases that control fundamental biological processes – they achieved interesting results. The studies were made on thale cress (Arabidopsis thaliana), a common weed found throughout the world. It is used as a model species because of its smaller genome.

“We found that a protein in thale cress called PROPEP is cleaved, releasing tiny protein fragments – small peptides that can trigger an immune-like response, warning unharmed cells in surrounding tissue. We also managed to understand how those peptides were generated. This was a major scientific breakthrough, and paved the way for the work I’m doing now.”

He realized there is much we do not know about the proteases and mechanisms that are activated when plants are damaged.

“We now know that metacaspases are activated by damage, and we want to understand more about the part they play in damage response. Yet we have also found protein substrate that we know has not been cleaved by metacaspase. We want to identify the proteases that have cleaved them and their importance to the plant when they react to damage.”

Damaging cells with laser

In the lab Stael and his research team culture the plants in petri dishes or in soil. They then crush them or compact them to cause specific types of damage. 

“Another, more drastic, way we achieve damage is to grind the plants down in liquid nitrogen. We also use lasers to inflict minimal damage in cells. We can then use microscopy to study what happens in the cell itself and in the surrounding cells, to understand rapid response mechanisms triggered by damage. We’re studying mechanisms that are activated from seconds and minutes up to one hour after damage occurs.”

Using proteomics (advanced methods used to study proteins), Stael can further explore plant tissues before and after damage, and identify the proteins that are cleaved. This work is being done in collaboration with SciLifeLab in Stockholm. In addition to thale cress, they will be studying liverwort (Marchantia), a unicellular green algae (Chlamydomonas), wheat, spruce and poplar for the purposes of comparison. The most interesting proteases will then be studied in greater detail.

“We hope to show how various proteases are important at numerous levels and stages of the plant’s damage response process and survival. This fundamental work we are doing in the field of plant biology may ultimately be of benefit in applications and in other research fields. Much also remains to be explained about the role and function of proteases in humans and other animals,” says Stael.

Text Susanne Rosén
Translation Maxwell Arding
Photo Magnus Bergström