How plant roots communicate
The Danish plant physiologist Tonni Grube Andersen is one of this year's winners of the Sofja Kovalevskaja Award of the Alexander von Humboldt Foundation. With the award money of 1.65 million euros, he is setting up his own research group at the Max Planck Institute for Plant Breeding Research in Cologne. Andersen is particularly interested in how plants interact underground with their surrounding root microbes. Tonni Andersen moved to the University of Lausanne in 2014 as a postdoctoral fellow with a Marie Curie fellowship. In an interview, he explains why he is so intrigued by the plant root and how he wants to get to the bottom of its communication with the microbial roommates.
How do plants communicate with their surroundings underground?
From a human perspective, plants are quite subtle in their ways of communicating. They rely much more on “smell” than sound or movement. Plant roots can be considered an exceptionally sensitive “nose” that can “smell” how friendly bacteria, fungi or even other close-by plants are, dependent on which chemical signals it encounters in the soil. Based on this, the plant can make complicated decisions such as: Should I be scared? Should I be happy? Should I just grow one of my roots in a different direction? I find this extremely fascinating, and one of my research goals is to find out how specific cells in the roots are used to coordinate these decisions across the entire plant.
What role does the plant microbiome play and why has this microcosm come into the spotlight of current research?
Roots are in many ways similar to our gut system. They take up nutrients from their outer surroundings and move them inwards, whereas our guts take up nutrients from the intestines. Through recent research, it is becoming clear that the microbiome of both humans and plants is important for a healthy life. Similar to having a healthy microbiome in the guts, plants grow better in presence of a healthy microbiome as certain members help the plant with getting enough nutrients as well as aiding in defence against disease-inducing organisms. Both in humans and in plants, we are (literally) only just beginning to scratch the surface of how these associations are formed.
Can you describe some of your major findings in plant root biology?
As a Phd student, I worked on chemical defences in the model plant Arabidopsis thaliana. This plant is kind of a “little sister” to crop species such as canola and mustards that researchers use as it is much smaller and easier to handle. I was studying how Arabidopsis forms and distributes compounds that serve to defend the plant against herbivores and diseases. I found a mechanism on how the mother plant sends these chemicals to the seeds and to the roots. This led to a collaboration with the company Bayer, as these compounds can be harmful to cattle, and agriculture is interested in developing seeds with lowered amounts. My work led to a fascination with roots and eventually to my postdoctoral work in root development. During this time, I worked with barrier layers in roots and their function in nutrient uptake and plant physiology. My work led to some novel data on a specific cell type in roots termed “passage cells” on which my future work will be based. Both my PhD and postdoc work were published in the prestigious journal “Nature”.
What is your research focus in your emerging Kovalevskaja Award research group in Cologne?
My findings have revealed that individual plant cells can respond very specifically to input they receive from their surroundings. This gives me a very useful tool that I will apply to study plant-microbe interactions in a level of detail that has been hard to do so far. My work will focus on Arabidopsis as we have a great deal of genetic knowledge in this plant. However, legume plants such as soy bean (Glycine max) and Lotus (Lotus japonicus), form highly specialized mutually beneficial associations with bacteria, which, in exchange for sugar, provide the plant with nitrogen that they fix from the surroundings. These associations depend on special root structures called nodules. Another part of my research will focus on how these associations and structures form and are connected to the plant's transport system.
How relevant is your research for agriculture? How can plant breeders benefit from it?
Most agricultural traits are based on above-ground features (amount of seeds, plant height, weight, etc.). The underground parts, and in particular the root microbiome, is a treasure chest of undiscovered tools that can be used to optimize plant health and yield. Understanding how plants communicate with the surrounding bacteria to provide a more efficient usage of nutrients and a stronger resistance to diseases would therefore not only allow us to grow more food in less space, but do so with less use of artificial fertilizers.
Interview: Philipp Graf