cell mechanics

Move over Arabidopsis, there’s a new model plant in town

Bond LSC researchers showed for the first time ever that a grass, Setaria viridis, can receive 100 percent of its nitrogen needs from bacteria  when associated with plant root surfaces. This grass will now serve as model for research into biological nitrogen fixation that could benefit crop development. | Photo by Roger Meissen, Bond LSC

Bond LSC researchers showed for the first time ever that a grass, Setaria viridis, can receive 100 percent of its nitrogen needs from bacteria when associated with plant root surfaces. This grass will now serve as model for research into biological nitrogen fixation that could benefit crop development. | Photo by Roger Meissen, Bond LSC

By Roger Meissen | MU Bond Life Sciences Center

As farmers spend billions of dollars spreading nitrogen on their fields this spring, researchers at the University of Missouri are working toward less reliance on the fertilizer.

Less dependence on nitrogen could start with a simple type of grass, Setaria viridis, and its relationship with bacteria. The plant promises to lay groundwork for scientists exploring the relationship between crops and the fixing nitrogen bacteria that provide them the nitrogen amount plants need daily.

“In science sometimes you have to believe because we often work with such small microorganisms and DNA that you cannot see,” said Fernanda Amaral, coauthor and MU postdoctoral fellow at Bond Life Sciences Center. “Before this research no one had actually proved such evidence that nitrogen excreted by bacteria could be incorporated into plants like this.”

Fernanda Amaral, coauthor and MU postdoctoral fellow at Bond Life Sciences Center. | Photo by Roger Meissen, Bond LSC

Fernanda Amaral, coauthor and MU postdoctoral fellow at Bond Life Sciences Center. | Photo by Roger Meissen, Bond LSC

Biological Nitrogen fixation — where diazotrophic bacteria fix atmospheric nitrogen and convert it to ammonium — provides a free way for plants to alter and absorb the nutrient. Farmers have long known that legumes like soybean fix nitrogen due to the symbiosis with bacteria in the soil through development of nodules on their roots, but since grasses like corn and rice don’t form this specialized structures that relationship has been trickier to explore.

Yet in fact, this team’s experiments showed the grass Setaria viridis received 100 percent of its nitrogen needs from the bacteria Azospirillum brasilense when associated with plant root surfaces.

“I believed in these bacteria’s ability, but I was really surprised that the amount of nitrogen fixed by the bacteria was 100 percent,” Amaral said. “That’s really cool, and that nitrogen can make so much of a difference in the plant.”

Worldwide farmers used more than 100 million tons of nitrogen on fields in 2011, according to the United Nations Food and Agriculture Organization. In the same year, the U.S. alone produced and imported more than $37 billion in nitrogen.

This grass can serve as a simple model for research, standing in for grass relatives such as corn, rice and sugarcane to explore a similar relationship in those crops. This research, “Robust biological nitrogen fixation in a model grass–bacterial association,” was published in the March 2015 issue of The Plant Journal.

 

A nutrient, a nuclear reactor and a model plant

Proving that this grass actually uses nitrogen excreted from the bacteria took some clever experiments, a global collaboration and a nuclear reactor.

MU researchers in the lab of Gary Stacey, a Bond LSC investigator, partnered with scientists in Brazil and at Brookhaven National Laboratory in New York to find a robust plant model system.

They screened more than 30 genotypes of Setaria viridis grass, looking for a strong nitrogen fixing response when colonized with three different bacteria strains. They germinated the seeds in Petri dishes and inoculated those three days after germination with a bacterial solution. Then plants were transplanted into soil containing no nutrients. By eliminating nitrogen in the soil, the scientists were able to make sure that the bacteria was the only source of nitrogen for plant.

The team settled on Azospirillum brasilense bacteria, which has been used commercially in South America to improve crop plant growth. It colonizes the surface of the roots and showed the greatest amount of plant growth when associated with plant roots.

Proving that the bacteria truly fixed the nitrogen used by the plant, required exposing plants to radioactive isotopes at Brookhaven National Laboratory. That began with Nitrogen 13, an unstable radio isotope that showed exactly where and how quickly this nutrient was taken up from the bacteria.

A radio tracer chamber at Brookhaven National Laboratory was needed to test if Setaria viridis actually used nitrogen produced by the bacteria. The scientists allowed only one leaf to contact the radioactive nitrogen, so they could truly tell if it was being used. | Photo provided by Fernanda Amaral

A radio tracer chamber at Brookhaven National Laboratory was needed to test if Setaria viridis actually used nitrogen produced by the bacteria. The scientists allowed only one leaf to contact the radioactive nitrogen, so they could truly tell if it was being used. | Photo provided by Fernanda Amaral

“Nitrogen 13 is really sensitive matter with a half-life of less than 10 minutes, and we first thought there wouldn’t be that much nitrogen fixed by the plant,” Amaral said. “We administered Nitrogen 13 only on the roots, quickly scanned the samples and calculated how much of the nitrogen the plants assimilated based on the decay analysis of the tracer.”

This experiment, paired with several others, showed that this model grass truly incorporated the nitrogen released by the bacteria and metabolizes it in several components.

 

Model (plant) citizen

But why does a type of grass that doesn’t produce food matter so much?

The answer is time and simplicity.

“Corn is really good at responding to bacterial inoculation, but it’s very big and takes a long time to produce seeds and also the genome is complex,” said Beverly Agtuca, an MU Ph.D. student who worked on the study. “Setaria viridis is a small plant that can produce a lot of seeds faster, has a pretty simple genome and can serve as a model for research.”

That makes it perfect to explore how the plant actually uses its bacterial partners, and labs around the world are already using this plant model for research.

For the Stacey lab, the next step is to pinpoint the gene in the model grass that makes this possible.

“We want to identify the genes responsible for the interaction between plant and bacteria and meanly the ones involved with the nitrogen uptake,” Fernanda said. “We hope that will allow us to improve plant growth based on the gene to further study.” We believe that our findings can stimulate others studies at this area, which seems to be a promise plant friendly way to apply for promoting a sustainable agriculture, especially to crop systems including bioenergy grass.

Amaral and Agtuca work in the lab of Gary Stacey at Bond LSC. Stacey is a Bond LSC investigator and a Curators Professor of Plant Sciences in the College of Agriculture, Food and Natural Resources at the University of Missouri. Collaborators included researchers at Brookhaven National Laboratory, State University of New York, Federal University of Paraná in Brazil and Federal University of Santa Catarina in Brazil.

Funding for this project came from the National Institute of Science and Technology- Biological Nitrogen Fixation, INCT-FBN, the Brazilian Research Council, Ciência Sem Fronteiras Program, The Department of Energy and SUNY School of Environmental Science and Forestry Honors Internship Program.

Nerve cell communication mechanisms uncovered, may lead to new therapeutic approaches for neurodegenerative diseases

 

Story by Madison Knapp/ Bond Life Sciences summer intern

Simple actions like walking, swallowing and breathing are the result of a complex communication system between cells. When we touch something hot, our nerve cells tell us to take our hand off the object.

This happens in a matter of milliseconds.

This hyperspeed of communication is instrumental in maintaining proper muscle function. Many degenerative diseases affecting millions of people worldwide result from reduced signaling speed or other cellular miscommunications within this intricate network.

Michael Garcia, investigator at the Christopher S. Bond Life Sciences Center and associate professor of biology at the University of Missouri, conducts basic research to answer fundamental questions of nerve cell mechanics.

“In order to fix something, you need to first understand how it works,” Garcia said.

Garcia’s research illuminates relationships between nerve cells to find factors affecting function.  His goal is to provide insight on fundamental cellular mechanisms that aren’t fully understood.

Garcia’s research has been funded partly by the National Science Foundation and National Institutes of Health.

Technological advancements have made it possible to better understand disease development in the human body to create more effective treatments. Alas, a scientist’s work is never finished— when the answer to one question is found, ten more crop up in its wake.

Garcia’s research, which appeared in several journals including Human Molecular Genetics andthe Journal of Neuroscience Research initially sought to shed light on the neuronal response to myelination, the development of an insulating border around a nerve cell, called a myelin sheath, which is critical in rapid communication between cells.

Eric Villalon, a graduate student in Michael Garcia's lab at the Bond Life Sciences Center, examines results. The Garcia Lab is answering news questions in cell mechanics. | PAIGE BLANKENBUEHLER

Eric Villalon, a graduate student in Michael Garcia’s lab at the Bond Life Sciences Center, examines results. The Garcia Lab is answering news questions in cell mechanics. | PAIGE BLANKENBUEHLER

How it works: Rebuilding cell theory

Garcia’s early research disproved a long-standing hypothesis concerning this cellular feature.

Mammals’ nervous systems are uniquely equipped with myelination, which has been shown to increase conduction velocity, or the speed at which nerve cells pass signals. Low velocity is often associated with neurodegenerative diseases, so research exploring why could later have application in therapeutic technology.

In addition to myelination, cell size makes a big difference in conduction velocity — the bigger the nerve cells, the faster they can pass and receive signals. Garcia’s findings disproved a hypothesis that related myelination to this phenomenon.

The hypothesis, published in a 1992 edition of Cell, claimed that myelination causes a cellular process called phosphorylation which then causes an increase in the axonal diameter (width of the communicating part of a nerve cell), leading to faster nerve cell communication. Garcia found that myelination did cause an increase in axonal diameter, and myelination was required for phosphorylation, but that the two results were independent of one another.

To narrow in on the processes affecting axonal diameter, Garcia identified the protein responsible for growth.

Garcia followed earlier work, showing that one subunit controls whether there is growth at all with myelination, by identifying the domain of this protein that determines how much growth.

After clarifying this part of the process, a question still remains: If not to control myelination, why does phosphorylation happen?

 

Looking forward

Jeffrey Dale, a recent PhD graduate from Garcia’s lab, said current research is in part geared toward finding a connection between phosphorylation and a process called remyelination.

Remyelination could be key to new therapeutic approaches. When a cell is damaged (as in neurodegenerative disease) the myelin sheath can be stripped away. Remyelination is the process a cell goes through to replace the myelin.

Imagine you have a new wooden toy boat, painted and smooth. If you take a knife and whittle away all the paint and then repaint it—even exactly how it was painted before—the boat is not going to be as shiny and smooth as it was before. This is how remyelination works (or rather, doesn’t).  When nerve cells are damaged, the myelin sheath is stripped away and even after the cell rebuilds it, the cell can’t conduct signals at the same speed it was able to before.

“If you can learn what controls myelination, maybe you can improve effectiveness of remyelination,” Dale said.

Garcia said it is possible that revealing the mechanics involved in phosphorylation could lead to better treatments. In context of neurodegenerative diseases, the question why don’t axons function properly might be wrapped up in Garcia’s question: In healthy cells, why do they?

Supervising editor: Paige Blankenbuehler