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Unlocking the Power of Legumes

Inefficient

Posted Jul. 10, 2018

Scientists gain further insight into the inner-workings of legumes in hopes of helping the plants reach their potential to advance agriculture.

Farmers and ranchers know their crops and pastures need to eat. But many plants are like 2-year-olds. Give them a full plate of nutrients, and they’ll only take half. The rest goes to waste.

Excess nutrients run off into waterways. They give rise to overpowering algae populations downstream that disrupt ecosystems. Upstream, producers stand by helplessly as money and effort wash away.

To limit this cycle, farmers and ranchers look for ways to reduce their nutrient usage. They use soil tests to help them determine how much fertilizer is enough. Emerging technologies build upon these knowledge foundations to help them apply precisely the right type and amount at the right time.

At the same time, scientists are looking for solutions within the plants themselves.

They hope to coax plants into more efficiently using nutrients by their own natural abilities.

Legume Leadership

If the microscopic creatures in the soil gave a neighbor-of-the-year award, they would probably give it to the legume family.

Legumes, which include crops like soybean, clover and alfalfa, have long been used by farmers as part of their crop rotations and other soil-health-building practices. This is because of the plants’ unique ability to fix nitrogen.

Unlike other plants, legumes form specialized plant organs called nodules on their roots. Within these nodules live soil bacteria called rhizobia, which turn nitrogen naturally found in the air into a form of nitrogen (called ammonia) that plants can use. In exchange for food and shelter, the rhizobia provide their host legume with this natural nitrogen fertilizer. As a result, legumes do not require farmers to apply additional nitrogen fertilizers.

exampleLegumes, such as this cowpea, form specialized plant organs called nodules on their roots. Soil bacteria called rhizobia live within these nodules and provide nitrogen to the plant.

Like other plants, including grasses, legumes also form mutually beneficial relationships with mycorrhizal fungi in the soil. These mycorrhizal associations help the plant acquire phosphorus and other nutrients. This is increasingly important because phosphorus resources are finite and limited to a few countries worldwide.

While nitrogen is not limited, reducing the need for costly synthetic nitrogen fertilizers would benefit farmers and ranchers, the environment, and society.

Like all living creatures, the legume’s blueprint for life is harbored in its DNA. Somewhere deep within its genetic blueprint are instructions for enabling it to build above-average relationships with soil microbes.

“If we can better understand what is happening at the genetic level, we will ultimately be able to improve legumes’ natural abilities to efficiently acquire nutrients,” says Michael Udvardi, Ph.D., chief scientific officer.

Udvardi is one of two Noble researchers who, in 2017, received a four-year, $5 million grant from the National Science Foundation to continue the exploration of legumes.

Udvardi and Noble Professor Kiran Mysore, Ph.D., have teamed up with scientists from across the country to continue work funded by the National Science Foundation: Maria Harrison, Ph.D., from the Boyce Thompson Institute; Julia Frugoli, Ph.D., from Clemson University; Catalina Pislariu, Ph.D., from Texas Woman’s University; Janine Sherrier, Ph.D., from the University of Delaware; and Becca Dickstein, Ph.D., from the University of North Texas.

In previous work, the team screened thousands of plants to identify genes that allow legumes to interact with soil microbes and receive nitrogen and phosphorus from them. They’ll continue to identify and study these key genes with the new funding.

exampleBarbara Nova-Franco, Ph.D., a postdoctoral fellow, (left) and Katherine Chang, a 2017 Noble Summer Research Scholar in Plant Science, prepare Medicago truncatula plants for further study.

This research is made even more critical when viewed through the lens of dwindling phosphorus supplies.

“It’s not a question of if we’re going to run out of phosphorus but when,” Mysore says. “It’s very important that we help plants better use nutrients like phosphorus so we can extend our supply.”

It may take many years to turn new knowledge from this project into improved legume cultivars. However, in the long run, such knowledge should accelerate plant breeding efforts to improve legumes for agriculture.

“We know thousands of genes are involved in these symbiotic processes, but we don’t yet know what roles most of these genes play or which ones are most important,” Udvardi says. “This grant will enable us to answer these questions and contribute to advancing agriculture and reducing its environmental footprint.”

Plant Root System

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The Power and Problems of Phosphorus

Most people probably don’t think about phosphorus very much during their day. Or at all. But in the next few decades, phosphorus will be on everyone’s mind. This chemical element (with the symbol P) is essential for all life as it is part of many biological molecules. P thus plays a vital role in agriculture, supporting the growth of healthy, productive crops. Unfortunately, the world is running out of P resources.

Phosphorus is an element essential to both plants and animals. It is one of three nutrients commonly applied to soil as fertilizer to help plants grow. It plays roles in RNA and DNA, the cell membrane, and energy transfer reactions.

Estimates vary, but some scientists put minable phosphorus supplies at providing enough for only 30-40 more years.

9 countries control 90 percent of the world’s known phosphorus reserves: Algeria, China, Iraq, Jordan, Morocco, Russia, South Africa, Syria, and Western Sahara. Source: 2015 U.S. Geological Survey report.

Crops in the southern great plains do not use about 22% of the phosphorus fertilizer they receive. The highest losses were from corn and cotton. Source: 2006 Natural Resources Conversation Service report.

Noble principal investigator Wolf Scheible, Ph.D., is exploring the molecular basis of how plants can more effectively use phosphorus.

Unabsorbed phosphorus remains in the soil, where it becomes either tightly bound or is used by microbes, or, through eluviation and erosion, it enters rivers, lakes and seas.

Phosphorus is not available in nature on its own, but is found in sedimentary and magmatic deposits, mostly as mineral rock phosphate.

Noble principal investigators Michael Udvardi, Ph.D., and Kiran Mysore, Ph.D., are studying the genes that allow legumes, like clovers and soybean, to efficiently acquire nitrogen and phosphorus.

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