Discovery Unlocks Key to Increasing Soybean Nitrogen Fixation

Soybean photos from MI Soybean College 2014. ( Aimee Cope )

Soybeans are an amazing plant—they fix their own nitrogen, thus reducing the cost of this particular input for farmers. For those farmers who do apply nitrogen, it might actually repress the plant’s ability to create nodules, according to a recent study at Purdue University.

“People tend to add fertilizer nitrogen to increase soybean yield, but that is not an economical solution because the fertilizer represses nodule formation,” said Jianxin Ma, professor at Purdue’s department of agronomy. “To increase the plant’s yield potential, it is important to increase the efficiencies of nodulation and nitrogen fixation.”

In a recent experiment, Ma and his team discovered a new method to increase nodule formation based on RNA in rhizobia, a soil-borne bacterium that assists with nodule formation. The rhizobia can ‘hijack’ soybean genes that suppress nodule formation.

“Controlling these processes could increase the amount of atmospheric nitrogen a legume could fix and improve yields,” he said. Ma’s team identified the soybean genes responsible for repressing nodule formation and use rhizobia, in conjunction with small RNAs, to turn off those undesirable genes.

In studies they proved this method resulted in a greater number of root nodules in soybeans. This means plant breeders could one day create soybeans with the ability to fix more atmospheric nitrogen—leading to potentially higher yields and less fertilizer needs.

“For the first time, we’ve demonstrated the function of bacterial small RNAs in cross-kingdom communication,” Ma said. “This may spur new research toward the understanding of widespread symbiotic relationships such as that between bacteria and the human digestive system.”

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