28. March 2019

The winner of the DNRF Photo Competition 2019: Root nodules can hold the key to a sustainable agriculture

  • The DNRF Photo Competition 2019: The three winning photographs in the Danish National Research Foundation’s Photo Competition 2019 have been found. In a series of three articles, the winners talk about their images and the research behind them. This article is about the first place winner, which this year went to senior researcher Niels Sandal. The articles about the second place winner can be found here and the third place winner here. More information about the competition can be found here.

  • The Panel’s Review: The photo is magical and not immediately open to interpretation. It is not possible to see whether the scale is at a cellular level or a cluster of galaxies, but the observer is drawn to the world that opens up in the picture. Further, the photo is very beautiful and well composed, and it gives a sense of movement and space. The scientific content is important as it shows how the scientist works with the symbiosis between bacteria and plants, which thereby can grow without addition of nitrogen fertilizer.



    • Christine Buhl Andersen, Director at Ny Carlsberg Glyptoteket
    • Louise Wolthers, Research Manager/Curator at the Hasselblad Foundation
    • Minik Rosing, Professor at the Natural History Museum, board member at the DNRF and Louisiana Museum of Modern Art

The subject of this year’s winning photo in the DNRF Photo Competition 2019 looks like something found in the far away areas of the universe, but in reality, the picture shows something as earthly as two nodules on the root of the plant Lotus japonicus. This plant forms a special symbiosis with soil bacteria, which makes the plant independent of nitrogen fertilizer, a quality that researchers dream of transferring to other plants in the hope of creating the sustainable agriculture of the future.

Two root nodules, Photo: Niels Sandal - The photo shows two nodules on the root of the leguminous plant Lotus japonicus. This plant exists in a symbiosis with the earth bacteria Mesorhizobium loti. In the symbiosis the bacteria obtain carbohydrates from the plant, and the bacteria deliver fixed nitrogen to the plant. Therefore, the plant can do without nitrogen fertilizer. The bacteria are colored with LacZ (dark blue), and the plant’s cell nuclei are colored with DAPI. The nuclei are seen as light blue dots. You can see the bacteria in the young nodule and on the surface of the older nodule. In our research group, we have isolated many of the plant genes that are necessary for symbiosis.
Two root nodules, Photo: Niels Sandal

Surrounded by darkness, a large blue-violet and luminescent bubble with a smaller and more bluish bubble in the background is seen in the jury’s winning photo in the Danish National Research Foundation’s Photo Competition 2019. Although the subject of the winning picture reminds one of a star cluster or foreign and indefinable celestial bodies far out in the universe, the picture actually shows something much more down to earth – literally.

“What we see in the picture are two nodules on the root of the plant Lotus japonicus. To the right is a young nodule not fully grown yet, and to the left we see a fully grown nodule. It is a microscopy image, and the small, light blue, almost white, dots in the large root nodule on the left are the cell nuclei of the plant, which fluoresce after staining with DAPI-color. The dark blue patches on the nodules show the soil bacterium Mesorhizobium loti, which is colored with the enzyme LacZ,” explained the man behind the winning picture, senior researcher Niels Sandal from Aarhus University.

Symbiosis between plant and bacteria makes artificial fertilizer unnecessary

Lotus japonicus is a legume, and most legumes have the special feature of being included in symbiosis with soil bacteria called Rhizobium bacteria. The symbiosis benefits both parties, as the bacteria have the ability to convert nitrogen from the air to ammonium, which can be absorbed into the plant as fertilizer, and vice versa; the plant provides nutrients in the form of carbohydrates to the bacteria. Where plants often defend themselves against bacteria, because they are harmful, legumes such as Lotus japonicus thus welcome the soil bacteria, because the bacteria are beneficial.

The symbiosis is especially interesting for the researchers, because Lotus japonicus, with the help of the bacteria, can live in soil without nitrogen, and thus, the plant does not need artificially produced nitrogen fertilizer to thrive. Today, huge amounts of energy are used in the production of nitrogen fertilizers to emulate the symbiosis mechanisms industrially. Therefore, in order to contribute to a more sustainable agricultural form, the researchers’ ultimate dream is to transfer the plant’s properties to other plants.

“If we can transfer the properties to, for example, grain plants such as corn, this will mean that the plants can grow in depleted and nitrogen-poor soil without the help of fertilizers. If we could mimic the symbiosis and remove the need for fertilizer, the nitrogen will be bound directly in the plant, thus making it easier to avoid fertilizer spreading in the soil and leaching to groundwater and watercourses,” explained Sandal, who emphasizes that there is still a very long way to go before the dream can come true:

“We are still taking the first steps along the way, but even small steps create major research development. This is the case with basic research. In the research group I have been a part of, we have built up tremendous knowledge about Lotus japonicus and the basic mechanisms of the symbiosis. You have to have that kind of knowledge before we can start to imagine transferring the properties to other plants,” he said.

(Video only available i Danish):

The symbiosis is investigated in the genes of the plant

Sandal has been working with Lotus japonicus for more than 20 years as part of Professor Jens Stougaard’s research group at Aarhus University.  Based on his research into the symbiosis of legumes and soil bacteria, Stougaard is today recognized as one of the world’s leading molecular biologists and has, over time, received a number of major research grants from, among others, the European Research Council and the Bill & Melinda Gates Foundation, and a grant from the Danish National Research Foundation to the basic research center CARB, which ran from 2007 to 2017.

As part of Stougaard’s group, Sandal has primarily dealt with the isolation of genes in Lotus japonicus. To ultimately transfer certain properties from one type of plant to another, the researchers have to understand how specific genes in the plant encode specific properties.

“In our research group I have been involved in isolating plant genes that are essential for the well-functioning symbiosis, including isolating genes for two receptors for a substance, which the bacterium produces as a kind of signal to the plant that it is okay that the bacterium is there. Before the soil bacteria enter the root through the root hairs, the substance is part of a signal exchange between plant and bacterium, which, so to speak, approves the presence of the bacteria and ensures that they are not there to parasite on the plant,” Sandal explained and continued:

“When the plant recognizes the substance with the help of the receptors, it causes the formation of the root nodules. The bacteria migrate through the root hairs to the nodules, where the bacteria begin to convert nitrogen to ammonium so that the plant can grow better.”

Researchers from all over the world use plant seeds from a greenhouse in Aarhus

In general, Professor Stougaard’s research group in fierce international competition has been among the leaders in uncovering large parts of the genetic and biological information of Lotus japonicus. Specifically, the research is based on, among other things, what Sandal and his colleagues, as part of the basic research center CARB, have for several years cultivated: various so-called mutated lines of Japanese bitch tooth. “Mutated” means that some of the genes no longer work. The researchers then look for whether the appearance of the plant has changed when a particular gene is mutated, thereby gaining knowledge of which processes the gene is important for.

“We had a greenhouse where we cultivated and worked with approximately 27,000 plants annually. Over time, we mapped the lines various DNA and genomes and collected seeds from the plants. Since then, we have put the knowledge we have about the lines in a publicly available database, where researchers from around the world can look for a line where exactly the gene they are interested in is mutated. Then they can order the plant seeds that we send out for free,” explained Sandal.

The database has contributed to spreading Lotus japonicus as a model plant within research in the legumes’ symbiosis with bacteria. Jens Stougaard was one of the first to start dealing with the symbiosis between Lotus japonicus and soil bacteria, and argued in the early 1990s that the plant would be a great model plant. The plant is suitable as a model because it has a small genome, it is self-pollinating, and it is not particularly large, so it can be grown on a large scale both in the laboratory’s petri dishes and in greenhouses. If you ask Sandal, it is the work to isolate the plant’s genes and the work on the various mutated lines that he is most proud of as having been a part of his career as a researcher:

“It is fundamentally important that we try to understand life on Earth biologically, and more specifically, it is potentially extremely important for the future of agriculture, if with our knowledge of Lotus japonicus, we can help to reduce or eliminate the use of energy-consuming artificial fertilizer. Therefore, I am happy and proud to have been involved in the groundwork that today forms the basis of our knowledge of the plant and the symbiosis with the soil bacteria,” Sandal concluded.

Read about the second place winner in this year’s competition here

Read about the third place winner in this year’s competition here

More information about this year’s competition can be found here

See the winning pictures of last year’s competition here

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