In small, bump-like nodules on roots in crops like soybeans and alfalfa, rhizobia bacteria produce the nitrogen that plants need to grow green and healthy. Scientists have wondered for years exactly how this mutually beneficial relationship works.
A discovery by a team of University of Missouri researchers could be the first step toward helping crops use less nitrogen, benefitting both farmers' bottom lines and the environment. Gary Stacey, an investigator in the MU Bond Life Sciences Center and professor of plant sciences in the College of Agriculture, Food and Natural Resources, found that crops, such as corn (maize), are "confused" when confronted with invasive, but beneficial, bacteria known as rhizobia bacteria. When the bacteria interact correctly with a crop, the bacteria receive some food from the plant and simultaneously produce nitrogen. In his study, Stacey found that many other crops recognize the bacteria, but do not attempt to interact closely with them. The journal
Science published the research this month (see article
abstract)..
"The problem is that corn, tomatoes and other crops have a different response and don't support an intimate interaction with the rhizobia, thus making farmers apply larger amounts of nitrogen than might otherwise be necessary", Stacey says. "Scientists have known about this beneficial relationship since 1888, but it only exists in legume crops, like soybeans and alfalfa. We're working to transfer this trait to other plants like corn, wheat or rice, which we believe is possible since these other plants recognize the bacteria".
When legumes like soybeans sense a signal from the bacteria, they create nodules where the bacteria gather and produce atmospheric nitrogen that the plants can then use to stimulate their growth. This reaction doesn't happen in other plants. "There's this back and forth battle between a plant and a pathogen," said Yan Liang, a co-author of the study and post-doctoral fellow at MU.
In the study, Stacey and Liang treated corn, soybeans, tomatoes and other plants to see how they respond when exposed to the chemical signal from the rhizobia bacteria. They found that the plants did receive the signal and, like legumes, inhibited the normal plant immune system. However, soybeans, corn and these other plants don't complete the extra step of forming nodules to allow the bacteria to thrive.
"The important finding was that these other plants didn't just ignore the rhizobia bacteria", Stacey says. "They recognized it, but just activated a different mechanism. Our next step is to determine how we can make the plants understand that this is a beneficial relationship and get them to activate a different mechanism that will produce the nodules that attract the bacteria instead of trying to fight them".
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Source: University of Missouri