Host plants reprogram their root cells to accommodate symbiotic nitrogen-fixing bacteria

February 17, 2014
Host plants reprogram their root cells to accommodate symbiotic nitrogen-fixing bacteria

To enter into symbiosis with nitrogen-fixing bacteria, host plants reprogram their root cells. An LMU team has now identified a calcium-binding protein complex that can be persuaded to spontaneously induce the formation of root nodules.

In almost all ecosystems, plant growth rates are limited by the availability of fixed nitrogen. Symbiotic interactions between plants and bacterial species that are capable of converting the in the atmosphere into ammonium ions, which plants can use as a source of nitrogen, are therefore of great agronomical significance. Legumes accommodate their symbionts in special organs called root nodules, which are normally induced only if the corresponding bacteria are present in the vicinity of the roots.

"In response to the presence of the symbionts, root cells respond with regular oscillations of the calcium concentration in their nuclei. These are thought to act as the signal for the root cells to enter symbiosis and initiate cell divisions to form root nodules," says LMU geneticist Martin Parniske. Together with members of his research group, Parniske has identified a which plays a crucial role in translating these signals into a specific pattern of gene activity that leads to the development of root nodules.

Spontaneous root-nodule formation

"We were able to show that a protein called CYCLOPS, whose function had remained enigmatic for many years, is involved in the redirection of cell differentiation," says Parniske. CYCLOPS is a component of a protein complex that interprets the calcium signals and, as a consequence, activates genes required for the establishment of the symbiosis. The calcium signal is detected by another protein in the complex, a kinase enzyme that is activated by calcium ions and, as a result, transfers phosphate groups onto specific sites in the CYCLOPS protein. This phosphorylation reaction confers on CYCLOPS the ability to bind to specific nucleotide sequences in the genome, thus activating a particular set of genes. The protein products of these genes are in turn responsible for the subsequent development of root nodules.

"Nothing in its amino-acid sequence had indicated that CYCLOPS acts as a transcription factor; it represents a previously unknown class of these proteins," Parniske explains. Further studies showed that CYCLOPS can even induce the spontaneous formation of root nodules – in the absence of the symbionts – if the phosphorylatable sites are chemically modified to mimic the presence of a phosphate group.

"This important finding proves that CYCLOPS plays a key role in reprogramming for symbiosis," Parniske points out. "It also makes it a useful tool for biologists who are trying to transfer the root-nodule symbiosis to plants that are unable to fix nitrogen, such as wheat or other economically important crop plants." Since the production of nitrogen fertilizers is fossil fuel consuming, this prospect is of great interest for sustainable agriculture.

Explore further: Evolution of root nodule symbiosis with nitrogen-fixing bacteria

More information: "CYCLOPS, A DNA-Binding Transcriptional Activator, Orchestrates Symbiotic Root Nodule Development." Sylvia Singh, Katja Katzer, Jayne Lambert, Marion Cerri, Martin Parniske. Cell Host & Microbe - 12 February 2014 (Vol. 15, Issue 2, pp. 139-152) DOI: 10.1016/j.chom.2014.01.011

Related Stories

Blossom end rot: Transport protein identified

November 23, 2011

Poor calcium distribution in agricultural crops causes substantial loss of income every year. Now a Korean-Swiss research team under the co-leadership of plant physiologists at the University of Zurich identified a protein ...

Life scientists differentiate microbial good and evil

January 9, 2014

(Phys.org) —To safely use bacteria in agriculture to help fertilize crops, it is vital to understand the difference between harmful and healthy strains. The bacterial genus Burkholderia, for example, includes dangerous ...

Recommended for you

Male seahorse and human pregnancies remarkably alike

September 1, 2015

Their pregnancies are carried by the males but, when it comes to breeding, seahorses have more in common with humans than previously thought, new research from the University of Sydney reveals.

Parasitized bees are self-medicating in the wild, study finds

September 1, 2015

Bumblebees infected with a common intestinal parasite are drawn to flowers whose nectar and pollen have a medicinal effect, a Dartmouth-led study shows. The findings suggest that plant chemistry could help combat the decline ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.