Rooting out plant responses

Legumes respond to nitrogen in their soil environment by putting the brakes on a symbiotic partnership with soil bacteria that helps produce more of the element.

A University of Tsukuba-led study revealed a key genetic pathway behind this response — a finding that could help enhance crop yield and reduce fertilizer use for those who want to breed soybeans and other commercially important legumes.

Tsukuba researchers raised the legume Lotus japonicas, a popular model plant for genome studies, in cabinets with a bacterium that invades the plant roots and forms bulb-like nodules. This bacterium then converts nitrogen from the air into a form usable by plants in exchange for energy from its legume host.

By exposing the plants to a chemical that modifies their DNA, the researchers pinpointed a mutant gene, NRSYM1, in which the nitrogen-fixing mechanism is defective. This gene, the authors showed, induces the production of a peptide that quells the formation of new root nodules when nitrogen is already abundant in the soil.