Plant biologists at the University of Illinois have identified the area of genomes within nitrogen-fixing bacteria in roots (rhizobia) that's being altered when the plant they serve is exposed to nitrogen fertilizer. Katy Heath, Illinois professor of biology, conducted the study with Christie Klinger and Jennifer Lau from Michigan State University. When they studied legumes at the W.K. Kellogg Biological Station in Michigan last year, the researchers determined that in fact, fertilizer caused rhizobia to become less beneficial to the plants they served. The new study was launched to determine why that was so.

In the new study, the researchers sequenced samples from a control group and from the nitrogen-fertilized group, where they located a key region of the genome that appears to be differentiated between those two groups. They found the difference in an area called the symbiosis plasmid, an area of extra chromosones in rhibozia that enables them to be mutually beneficial with the plants, and where the gene is located that actually breaks the bond between nitrogen molecules and the air to "fix" it into ammonium that the plant can use. At that region of the genome, the differentiation suggests that the effects of nitrogen fertilizer were to make the less beneficial rhizobia different than the controlled rhizobia at that location.

For more details, read the news release at the University of Illinois website.

Figure: University of Illinois plant biology professor Katy Heath and her colleagues pinpointed the area of genomes within nitrogen-fixing bacteria in plant roots that’s being altered when the plant is exposed to nitrogen fertilizer. (Photo by L. Brian Stauffer.)