Inaugural lecture by Saskia van Wees: "Plants are anything but defenceless creatures"

When plants are attacked by insects or threatened by harmful microorganisms, they may seem to endure this passively. However, plants are anything but defenceless: they are able to fend off most threats. Professor Saskia van Wees investigates the intricacies of plant resistance and the role plant hormones play in these processes. Her research aims to pave the way towards a world free of chemical pesticides. Today, she delivers her inaugural lecture.

While studying biology in Utrecht, many of Van Wees's classmates decided to go into a medical direction. But Van Wees chose a different path. “I have always been a bit contrarian," she says. "I believed I could make a greater impact by focusing on plants and food security.”

Plant diseases may pose a serious threat to food security and, in turn, the livelihoods of countless people. Van Wees: “Take the potato disease that caused the infamous Irish famine in the 19th century. It led to the death of a million Irish people and forced 1.5 million more to flee to America.”

We now understand that plants have a flexible, hormone-regulated defence system that enables them to protect themselves against all kinds of attackers.

Hormones

Van Wees and her research team are now investigating how plants protect themselves against potential threats. Plant cells detect microorganisms using receptors—proteins on the cell surface that bind to fragments of these microorganisms or to components of plant cells damaged by them.

As soon as a plant detects microorganisms or damage, it triggers a defence response. Two plant hormones, salicylic acid and jasmonic acid, determine how this response unfolds. Salicylic acid primarily manages defences against pathogens that extract nutrients from living plant cells. In contrast, jasmonic acid governs defences against pathogens that destroy plant cells to access their nutrients. Jasmonic acid also plays a critical role in responding to cell damage caused by insect attacks.

Combining breeding based on resistance proteins with strengthening hormone-regulated defences could offer a sustainable solution.

Flexible immune system

As a PhD candidate in the 1990s, Van Wees discovered that salicylic acid and jasmonic acid influence each other, ensuring that the plant's defence response is tailored to the specific attacker it faces. Later, she and her colleagues found that two additional hormones, abscisic acid and ethylene, modulate the responses to salicylic acid and jasmonic acid, further shaping the regulation of the plant's defences.

These findings still have great impact on Van Wees's research and that of many plant scientists worldwide. Van Wees: “We now understand that plants have a flexible, hormone-regulated defence system that enables them to protect themselves against all kinds of attackers.”

Pesticides

Chemical pesticides are still widely used to combat plant diseases, but Van Wees points out that we should minimize their use, as they often have harmful side effects on soil health, insects, and humans.

To reduce pesticide use, the agricultural sector is often focused on developing plant varieties with so-called resistance proteins. Harmful microorganisms that cause disease have evolved substances that they inject into plant cells to suppress the plant's defence response. In turn, plants have developed resistance proteins that can recognize these injected substances, after which a strong immune response is triggered after all.

In fact, I would go as far as to say that all plant researchers, even if they don't realize it yet, are working on hormones.

Combination

However, Van Wees argues that the focus should also be on plant hormones. “Microorganisms are present in great numbers and have short generation times, allowing them to adapt quickly to plants and their proteins. As a result, resistance proteins lose their effectiveness relatively fast, requiring the constant development of new plant varieties with new resistance proteins. But if we enhance plant resistance through hormone-regulated defences, the plant can produce more defence weapons when an infection occurs, helping to inhibit the infection. This approach not only works against specific pathogens, but also offers protection against new variants or even entirely new diseases. Therefore, combining breeding based on resistance proteins with strengthening hormone-regulated defences could offer a sustainable solution.”

Gene expression

To strengthen hormone-regulated defences, it’s crucial to first understand how they work. After all, how can just a few hormones have such diverse effects?

Van Wees explains that when the concentration of a hormone increases, for example due to an infection, various genes can be "turned on". This means DNA is transcribed into RNA, which is then translated into protein. Van Wees: “When I started this research, we could only measure whether individual genes were turned on. But thanks to advances in technology, we can now track all genes simultaneously.”

Artificial intelligence

After a pathogen or insect is recognized, various hormones are produced at different times and in different amounts. Van Wees and her team investigate which genes are activated by these hormones in response to insect predation, pathogen infection, and environmental stressors like drought. They also study what happens when plants face a combination of stress factors, such as both infection and drought. Doing so, they focus on how gene regulation changes over time.

These studies generate a large amount of complex data. To make sense of it, Van Wees has recently begun collaborating with researchers at the University of Amsterdam, who are applying the latest advancements in artificial intelligence to help unravel the data.

All plant researchers

In her inaugural lecture, Van Wees highlights the crucial role plant hormones play in nearly every process within a plant. Van Wees: “In fact, I would go as far as to say that all plant researchers, even if they don't realize it yet, are working on hormones.”