Scientists have found an evolutionary innovation in soybean that could raise yields if fine-tuned through gene editing, according to a study published this month in the Proceedings of the National Academy of Sciences, The Fence Post reports from Purdue University materials. Legumes pull nitrogen from the air through rhizobia bacteria housed in root nodules; 'this study reports a new mechanism that promotes soybean nodulation, plant productivity and environmental resilience,' said Purdue agronomist Jianxin Ma, who co-led the work with Blake Meyers, director of the Genome Center at the University of California, Davis.

In 2019 Ma's team showed that rhizobia send tiny RNA fragments into plant cells that act like dimmer switches on plant genes, helping the plant form more nodules. The new paper finds the complementary mechanism on the plant's side — an 'accelerator pedal' that promotes nodulation and nitrogen fixation and can raise yield under low-nitrogen conditions, while keeping the system balanced: too many nodules cost the plant energy, too few starve it.

Two signalling molecules coordinate it. Soybean roots produce a small peptide that moves up through the xylem to the shoots, where it regulates production of a specific microRNA; the microRNA travels back to the roots to suppress a soybean gene, completing a relay. 'Signals are sent from leaves to roots and back again,' Meyers said. 'With these insights, we may be better able to optimize a natural process of nitrogen fixation and reduce our dependency on expensive fertilizer, at least for soybeans.'

The mechanism is present in the soybean crop species and in common bean but absent from two model legumes widely used in research — an innovation that arose after the crop lineages diverged millions of years ago, which argues for studying crops alongside models. Ma used gene editing to modify the microRNA pathway for stronger nodulation, a technology with a patent pending that could complement rhizobia seed treatments and field sprays farmers already use.

In the 1980s variety Williams 82, no longer grown commercially, the modification improved seed quality and protein content; Purdue's technology-commercialisation office has signed testing agreements with potential licensees to see whether the gains transfer to elite varieties. Co-first authors were postdoctoral scientists Jingbo Duan, Jinbin Wang and Runze Guo, with funding from the National Science Foundation, National Institutes of Health, United Soybean Board, Purdue AgSEED and the Indiana Soybean Alliance. 'I'm particularly grateful to the soybean farmers in the U.S., including about 20,000 in Indiana,' Ma said.

Source: The Fence Post (Purdue University)