Plant researchers throughout the world have been trying for many years to find a substitute for fertilisers. An important step towards achieving this objective has now come from results obtained by plant researchers at the Department of Molecular Biology, the University of Aarhus. These results have just been published in the renowned journal Nature.

Atmospheric nitrogen (N2) cannot be taken up by plants, and they therefore depend on N2 being converted by other organisms or via chemical processes to a form that is accessible. Considerable amounts of fertilisers are produced all over the world, but a large part of the nitrogen conversion takes place in nodules on the roots of leguminous plants by means of symbiotic nitrogen-fixing bacteria. For many years, research laboratories around the world have been trying to find new ways of exploiting the special properties found in leguminous plants in a biotechnological context, and the group from Aarhus has now succeeded. 

Help to boost global food production

Lack of nitrogen is a significant barrier to adequate food production in many countries, and every time crops are harvested, nitrogen disappears from the nutrient cycle in the fields.

A number of leguminous plants are used in the rotation of crops to restore plant-accessible nitrogen to the fields, but there are cultivational, nutritional and cultural limitations to the percentage of leguminous plants used in this rotation. Plant breeders have therefore dreamt for years of developing other nitrogen-fixing basic crops. Developing rice, wheat and maize in particular, with the same ability to be part of the symbiosis with so-called nitrogen-fixing Rhizobium bacteria, would revolutionise global food production.

Although it has been possible for a number of years to use gene technology to transfer genes between different species, it is a very great challenge to transfer such a complicated process as the ability to be part of the symbiosis with another species of plant.Identifying the genes involved in the process is an important step along this path.The discovery that some of the genes crucial for establishing symbiosis are strongly preserved and found in many other organisms than leguminous plants provides hope that it will be slightly easier to transfer the symbiotic characteristics of Rhizobium bacteria to important crops.

Important discovery by Aarhus scientists

A few years ago, Professor Jens Stougaard's group at the University of Aarhus identified the genes that code for two proteins - so-called receptors - that recognise the Rhizobium bacterium as a symbiosis partner. This group has now discovered another important component in the development of nitrogen-fixing root nodules.

Leïla Tirichine, one of the scientists in the group, found some mutations in the leguminous plant Lotus japonicus (Japanese bird's foot) that are capable of making root nodules without Rhizobium bacteria being present. Aarhus researchers were subsequently able to identify the mutant gene. The ability to find both a plant mutation that spontaneously makes root nodules and the gene that causes this provides hope that it might be possible, in the long run, to start cell divisions leading to the formation of root nodules in plants that do not normally make them. If this can be done, it might also subsequently be possible to get Rhizobium bacteria to enter the nodules and start a nitrogen-fixing process. A large proportion of the conversion of nitrogen would thus be able to take place naturally, which would make it possible to drastically reduce the use of nitrogen fertilisers or ultimately do away with them altogether.

The Aarhus group is among the world leaders in this area of research, and it has therefore been possible for the group to attract skilled scientists to Aarhus from abroad. These include Leïla Tirichine from France, who is the first author of the article in Nature and was appointed as a researcher at the University of Aarhus by Professor Jens Stougaard. In addition to the department at the University of Aarhus, the research group behind these results also consists of scientists from universities and leading research institutions in Japan, Germany and the UK.

Leïla Tirichine also presented the group's results at a lecture at an international conference for plant researchers that was recently held at the Department of Molecular Biology at the University of Aarhus. 

More information

Read more about the results from the University of Aarhus (in Danish only) at Planteforskning.dk.

The title of the article published in Nature vol. 441, 1153-1156 (2006) is: Deregulation of a Ca2+/calmodulin-dependent kinase leads to spontaneous nodule development by Leïla Tirichine, Haruko Imaizumi-Anraku, Satoko Yoshida, Yasuhiro Murakami, Lene H.Madsen, Hiroki Miwa, Tomomi Nakagawa, Niels Sandal, Anita S.Albrektsen, Masayoshi Kawaguchi, Allan Downie, Shusei Sato, Satoshi Tabata, Hiroshi Kouchi, Martin Parniske, Shinji Kawasaki and Jens Stougaard.