plant science

Christopher Garner #IAmScience

Christopher Garner

Christopher Garner, Ph.D moments before his sucessful dissertation defense. | Photo by Mary Jane Rogers, Bond LSC

By Mary Jane Rogers | Bond LSC

“#IAmScience because I believe that the collective pursuit of scientific knowledge is what moves us forward as a species.”

In the time leading up to Christopher Garner’s dissertation defense, you never would have known if he was nervous. He was confident and composed, and the conference room at Bond LSC was completely filled with his professors, friends and well-wishers. Dr. Walter Gassmann gave a complimentary introduction to the dissertation, saying, “I don’t know if I’ve ever seen a student so prepared.” Needless to say, Garner passed with flying colors.

Garner completed his undergraduate degree at the University of Missouri, St. Louis. After graduating, he went to work on a small R & D team at a St. Louis company. That was his first experience with research and his mentor was influential in persuading Garner to go to graduate school. During graduate school at MU, Garner worked in Gassmann’s lab at Bond LSC, researching the inner workings of the plant immune system. His favorite part of working in the lab was constantly conducting new experiments.

“It’s really satisfying to make a prediction and then see it come true,” said Garner. “It can be equally exciting to see things are radically different than what you predicted.”

His dissertation – “Should I slay or should I grow? Transcriptional repression in the plant innate immune system” – focused on the tradeoffs between growth and defense that plants face when mounting an immune response. While the immune response is essential for the survival of plants in the face of pathogen infection, expression of defense-related genes can interfere with growth and development and must therefore be kept under tight control. His research identified a protein involved in preventing an overshoot of the immune system after it has been activated, thereby contributing new information to the field.

“If there is some way in which I can contribute to the pursuit of scientific knowledge, be it through research or teaching others about science, then I feel like I have done something worthwhile,” said Garner.

Congratulations on a successful defense, Chris!

The gall of it

How bossy insects make submissive plants create curious growths

By Samantha Kummerer | Bond LSC

They are bumps on leaves, bulges in stems and almost flower-like growths from plant tissue with a striking amount of variety. They are galls.

These unnatural growths garnered the curiosity of Jack Schulz for years. While he’s spent 40 years studying topics from Insect elicitors to habitat specialization by plants in Amazonian forests, what he’s really wanted to study was galls.

“It’s so weird,” said Schultz, director of the Bond Life Sciences Center. “I’ve always been really curious about how these strange structures form on plants.”

Schultz has spent the last two years trying to answer that question, looking at their development and the underlying genetic changes that make galls possible.

He’s not alone in his fascination.

“I found my very first gall when I was a masters student,” said Melanie Body, a postdoctoral researcher in Schultz’s lab. “I was really excited because it was here the whole time, I just didn’t see it. One of my teachers showed me and it was like a revelation, basically, what I wanted to work on.”

These “strange structures” are often mistaken for fruit or flower buds on a variety of plants from oak trees to grapevines and there’s a good reason why…

“A gall on a plant is actually, at least partly, a flower or a fruit in the wrong place,” Schultz said.

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Galls on a leaf. The leaf’s red bumps are not natural, but caused by tiny insects. Inside each gall is many tiny insects. | photo by Melanie Body

These galls can be the size of a baseball or the size of a small bump depending on the plant. They can also range from just small green bumps on the undersides of leaves to vivid complex growths of color.

Despite the variety, the one thing consist across plants is that the gall is not there by the plant’s choice.

“The insect has a pretty good strategy because it starts feeding on the plant and it will create a kind of huge structure, huge organ, where it can live in, so it’s making it’s own house,” Body said.

The reasoning behind the formation is relatively unknown, however, it is hypothesized that the insect flips a switch within the plant. The insect is not injecting anything new, but rather turning off and on certain genes within the plant.

Schultz explained the galling insect has the power to changes the expression of genes and in some instance disorient the plant’s determination of what is up from down.

 

The Problem

So how does this affect the plant?

Not only is the insect creating the gall against the plant’s nature, it is also using the plant’s energy and materials for the job.

“I think it’s very cool to imagine an insect can hijack the plant pathway to use it for its own advantage,” Body said.

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The view of a gall from under a microscope. The mother insect is the orange figure in the foreground and is surrounded by her eggs. | Photo by Melanie Body

The insect receives protection and a unique food source and in turn, the plant is left with fewer resources.

“From the plant’s point of view that’s all materials that could have gone into growth and reproduction, so you can think of these galling insects as competing with the plant they’re on for the goodies the plant needs to grow and reproduce,” Schultz explained. “That’s not so good for producing grapes.”

Grapevines are just one of the many plants that galls can form on, but also the plant Schultz’s research uses.

“In our case we work on grapes, so it can be a big issue if the fruits are not sweet enough anymore, because if you don’t have sugar in the fruit then it’s not good enough for the wine production, so it’s pretty important,” Body explained.

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Researcher Melanie Body searches the grapevines for galls at Les Bourgeois Vineyards. | Photo by Samantha Kummerer, Bond LSC

In Missouri, the story of grapevines and galls goes back to the 1800’s.

The story goes, the phylloxera insect found its way over to France. Soon it spread throughout the country; wiping out vineyard after vineyard.

“The great wine blight and the world was going to lose all wine production because of this pest,” said Schultz.

Luckily, a small discovery in native Missouri grapevines led to a solution that allowed wine drinkers to rejoice and scientists to puzzle.

“There’s something about the genes in Missouri grapevines that protects them against this insect,” Schultz explained.

While the European wine industry faced extinction, the phylloxera insect, coexisted with native Missouri grapevines. So, now every grapevine in a vineyard is grafted with insect-resistant roots from Missouri grapes.

But, no one really understands what’s so special about grapevine roots in Missouri.

 

The research

These galls aren’t new. They’ve actually existed for up to 120 million years. But, here’s what is:

“When we started this research, we thought this is a really well-studied insect,” Schultz said. “It turns out there is an awful lot we don’t know about them.”

The team collects samples of galls from grapevines at Les Bourgeois. Back in the lab the galls are dissected using very small tools and then examined with a microscope. Under the microscope, a colony of the insects emerges. The otherwise miniscule mother insect and her 200 eggs can be seen alongside other insects just moving around the gall.

Researcher Melanie Body examines a grapevine gall under a microscope. Body is a member of Jack Schultz’s lab that studies galls and the insects that create them. | Photo by Samantha Kummerer, Bond LSC

Body compares the insects’ round textured bodies to oranges but with two black eyes.

Schultz’s team hypothesized that there are specific flower or fruit forming genes that are necessary for the insect to create a gall.

To answer this, the team looks at which genes are turned on when the insect creates the formation of a gall. Those observations by themselves don’t prove which genes are essential. So, next, the researchers manipulate the genes by changing the gene’s expression.

“If we find that Gene A is always on when the insect causes a gall to form, we can stop the expression of Gene A to test the hypothesis that it needs gene A to get the gall to form,” Schultz explained. “We can ask a plant. If you lack Gene A, can our insects still form galls?”

The researchers are still analyzing the results, but the current findings suggest that some genes do reduce the insect’s ability to make a gall.

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A microscopic view of a galling insect in the process of creating a gall. The gall is forming around the insect. | Photo by Melanie Body and David Stalla

Since beginning the research two years ago, Schultz said he has discovered, “all kinds of crazy things”.

Schultz said it was previously believed that the insect was staying in one place when making the circular gall, but actually, the little insect is moving around; something no one realized before.

And that’s not the only myth this research is debunking. For example, many believe there is one insect per gall, but this turns out to be incorrect. The gall can actually become a hospital of sorts where many mother insects flock to move in and lay their eggs.

And although galls sounds like an odd area of study, the research actually falls under basic developmental biology.

Schultz said research on galls could lead to discoveries about flowering and fruiting.

“Finding a situation in which flower or fruit structures are forming in odd places is actually suggesting to us, pathways and signals that are probably not as well studied in developmental – normal flowers and fruits,” Schultz said.

Beyond curiosity, one of the reasons to study the galls is to find a way to reduce the number of pesticides used on grapevines. The small size of the galling-insect causes grape growers to spray a lot of chemicals.

There’s a lot of discoveries, a lot of implications, but also still a lot of unknowns. Schultz doesn’t let that discourage him.

“If we knew everything about all kinds of things in nature, I’d be out of business and we’d have nothing to do,” Schultz reassured.

The curiosity behind the research continues to hold true for both Schultz and Body outside the lab. From collecting galls for each other to photographing the mysterious spheres, the two are always on the look out for the hidden work of the tiny insect.

“They’re everywhere,” Body said.

The next Martians: the common bean?

Researchers in the Mendoza-Cozatl lab grow beans in a soil that simulates Martian soil
By Eleanor C. Hasenbeck | Bond Life Sciences

As NASA works to send people to Mars, researchers at the Mendoza-Cozatl lab at Bond Life Sciences Center are exploring the possibility of sending beans to the red planet. The journey from Earth to Mars alone would take somewhere between 100 to 300 days. To feed astronauts on these longer missions, scientists are studying space horticulture.

Norma Castro, a research associate in the lab, studies how common beans grow in a soil that simulates Mars’ red soil. The common bean is a good candidate for interstellar cultivation. Beans are a very nutritious crop, and their affinity for nitrogen-fixing bacteria can improve soil health while requiring less fertilizer. Castro is trying to understand how different varieties of beans could grow in the soil.

“This kind of research not only will tell us the right plants to take to Mars, but also which kind of technology needs to be developed,” Castro said.

Scott Peck #IAmScience

Scott Peck

Scott Peck, a biochemistry professor at Bond LSC. | photo by Morgan McOlash, Bond LSC

By Mary Jane Rogers | Bond LSC

“#IAmScience because I want to discover. I want to ‘see’ – by understanding – things that others haven’t ‘seen’ before.”

Every day we make decisions based off on what we encounter in the environment. Plants do the same thing. Scott Peck, a Chicago-area native, is a biochemist who studies how plants translate information they receive about the environment (such as changes in light and temperature) into their own chemical “decisions”, also known as signal transduction. For him, it’s about making biology into a puzzle. Put the right pieces together, and you find ways to create more resistant crops or more effective antibiotics. With today’s technology and Peck’s passion for plant communication, anything could be possible.

Unmasking the unknown

Scientists explore genetic similarities between plants and mice

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University of Missouri PhD Candidate Daniel L. Leuchtman peers through an Arabidopsis plant. Leuchtman has been experimenting with replacing a gene in the plants immune system with a similar gene from mice. | Photograph by Justin L. Stewart/MU Bond Life Sciences Center

By Justin L. Stewart | MU Bond Life Sciences Center

Almost two-thirds of what makes a human a human and a fly a fly are the same, according to the NIH genome research institute.

If recent research at the University of Missouri’s Bond Life Sciences Center is verified, we’ll soon see that plants and mice aren’t all that different, either.

Dan Leuchtman studies a gene in Arabidopsis plants called SRFR1, or “Surfer One.” SRFR1 regulates plant immune systems and tell them when they are infected with diseases or illnesses. Leuchtman studies this model plant as a Ph.D. candidate at MU, splitting time between the labs of Walter Gassmann and Mannie Liscum.

His research involves breeding Arabidopsis plants missing the SRFR1 gene and then replacing it with the MmSRFR1 gene.

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A series of Arabidopsis plants show the differences between the plants, from left, without SRFR1, with MmSRFR1 and with SRFR1. | Photograph by Justin L. Stewart/MU Bond Life Sciences Center

So, what is MmSRFR1? Leuchtman and company believe it’s the animal equivalent of SRFR1, though they aren’t fully aware of all of its’ functions.

“We’re actually one of the first groups to characterize it,” Leuchtman said.

Arabidopsis plants missing the SRFR1 gene struggle to grow at all, appearing vastly different from normal plants. Leuchtman says that a plant missing the SRFR1 gene is a mangled little ball of leaves curled in on itself. “It’s really strange looking.”

While his experiments haven’t created statuesque plants equal to those with natural SRFR1 genes present, the Arabidopsis plants with MmSRFR1 show a notable difference from those completely lacking SRFR1. Leuchtman says the plants with MmSRFR1 lie somewhere in between a normal plant and one lacking SRFR1.

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University of Missouri PhD Candidate Daniel L. Leuchtman poses for a portrait in a Bond Life Sciences Center greenhouse. Leuchtman has been experimenting with replacing a gene in Arabidopsis plants immune system with a similar gene from mice. | Photograph by Justin L. Stewart/MU Bond Life Sciences Center

“At its’ core, it’s more understanding fundamental biology. How do we work? How do organisms tick? How do you go from DNA in a little bag of salts to a walking, talking organism?” Leuchtman said. “The more you know about how an organism functions, the more opportunities you have to find something that makes an impact.”

What’s in the spit?

Bond LSC is now producing monthly segments for KBIA, Columbia’s NPR station at 91.3 FM.

This month highlights the work of Melissa Mitchum, a molecular plant nematologist at Bond LSC and an associate professor of Plant Sciences in the College of Agriculture, Food and Natural Resources.

She studies nematodes, a pest that cost soybean farmers billions of dollars each year. Her lab recently helped discover that this tiny parasite produces molecules that mimic plant hormones in order to siphon nutrients from soybean roots.

Tune in at 12:30 to hear her profile or visit the Soundcloud link above to hear the segment.

 

Putting down roots

Plant scientist Ruthie Angelovici joins the Bond Life Sciences Center

By Jennifer Lu | MU Bond Life Sciences Center

Ruthie Angelovici

Ruthie Angelovici

Ruthie Angelovici clearly remembers her big eureka moment in science thus far. It didn’t happen in a laboratory. It wasn’t even her experiment.

At the time, Angelovici was in college studying marine biology. She had spent a year going on diving trips to figure out whether two visibly different corals were polymorphs of the same species, or two separate species.

A simple DNA test told her the answer in one afternoon.

“That’s the day I decided that there was a lot to be discovered, just in the lab,” Angelovici said. She switched majors and hasn’t looked back.

Better Nutrition in Crops

Angelovici studies the molecular biology of plants.

As a newly minted assistant professor in biological sciences at the Bond Life Sciences Center, her goal is to increase the nutritional quality of staple crops like corn, rice, and wheat.

Although these crops make up 70 percent of people’s diet across the world, Angelovici said, they aren’t very nourishing.

Corn, rice, and wheat are deficient in several key nutrients called essential amino acids. For example, if a person lived on wheat alone, they would have to eat anywhere from three to 17 pounds of the grain per day to reach the daily recommended amount for these nutrients.

Moreover, harsh growing conditions cause amino acids levels in plants to plummet—an increasingly grave problem as the earth’s climate gets warmer.

“If you think about the future, we’re going to face more droughts, more heat,” Angelovici said. “We need to figure out how we can maintain quality under those circumstances.”

Scientists have been trying to improve the nutritional quality of crops for years, whether through classical breeding or genetic engineering. The latter requires knowing which genes to alter.

Angelovici uses a technique called genome-wide association mapping. This allows her to link the natural variations within a particular trait — say, a special type of amino acids that are branched in structure — with the genes that affect this trait.

In previous studies, Angelovici chose Arabidopsis thaliana, which is popular among plant scientists for its simple genome and short life cycle, as her model plant.

She collected seeds from 313 varieties and burst them open, one seed type at a time, to release their contents. After separating the free amino acids from the rest of the seed pulp, she measured the branched amino acid levels — as a ratio to each other and to other amino acids — to build a nutritional profile that acts like a fingerprint for each plant.

Angelovici used this fingerprint to identify plants that shared similar traits. Then she scanned their DNA for any small genetic variations, or mutations, that plants had in common.

When she tallied up the frequency of each mutation in what is called a Manhattan plot, she found one particular variation that outstripped the others, standing out like a skyscraper over a city: a small section on chromosome 1 close to a gene called bcat2.

Angelovici then switched this gene off. When branched amino acid levels changed, it suggested that this trait was linked to the bcat2 gene.

However, Angelovici warned that often plants resist genetic tinkering. They lose viability, or cannot germinate seeds.

“We get yield penalty,” Angelovici says, “and the question is why?”

Metabolism, she explains, is like a network. “If you pull one way, something else is going to be affected.”

That’s where bioinformatics comes in handy. Angelovici uses an approach called network analysis to look at many pathways within the plant at once. This allows her to see the big picture, as well as the fine detail.

Moving to Missouri

Angelovici has being studying plant metabolism for ten years. Originally from Israel, she earned her PhD in 2009 under Gad Galili at the Weizmann Institute of Science in Rehovot, Israel. Then, she continued her research as a postdoctoral fellow at Michigan State University.

She prefers working with plants to animals because plants are relatively easy to manipulate and breed. Also, she loves animals and at one point wanted to be a veterinarian.

Angelovici says she was immediately drawn to the University of Missouri, and is looking forward to collaborating with researchers at Bond LSC.

“There is a great program here, great plant people here,” she said. “So, Mizzou is spot on.”

Although she has found an undergraduate and a post-doctoral researcher to help her so far, the benchtops in her laboratory remain uncluttered save for some equipment, like glassware and a few gel boxes. Three pristine white lab coats hang neatly from hooks on the wall.

But Angelovici is not fazed by the enormous task of getting her lab up and running.

“I just love doing this. It’s like climbing a mountain,” Angelovici said, about the research process. “You do it slowly and then you feel like you’re going up and you are achieving more and you can see more. It’s really fulfilling.”

As for that big eureka moment, Angelovici says she doesn’t put much stock in it.

Then she laughs. “But maybe I will experience one, and then I’ll change my mind.”

Scientists uncover how caterpillars created condiments

The next time you slather mustard on your hotdog or horseradish on your bun, thank caterpillars and brassica for that extra flavor.

While these condiments might be tasty to you, the mustard oils that create their flavors are the result of millions of years of plants playing defense against pests. But at the same time, clever insects like cabbage butterflies worked to counter these defenses, which then started an arms race between the plants and insects.

An international research team led by University of Missouri Bond Life Sciences Center researchers recently gained insight into a genetic basis for this co-evolution between butterflies and plants in Brassicales, an order of plants in the mustard family that includes cabbage, broccoli and kale.

Chris Pires | Image by Roger Meissen, Bond LSC

Chris Pires | Image by Roger Meissen, Bond LSC

The team published these new insights online in Proceedings of the National Academy of Sciences (PNAS) in June.

“We found the genetic evidence for an arms race between plants like mustards, cabbage and broccoli and insects like cabbage butterflies,” said Chris Pires, an MU Bond Life Sciences Center researcher and associate professor of biological sciences in the College of Arts and Sciences. “These plants duplicated their genome and those multiple copies of genes evolved new traits like these chemical defenses and then cabbage butterflies responded by evolving new ways to fight against them.”

A biting taste

While you might like the zing in mustard, insects don’t.

Compounds, called glucosinolates, create these sharp flavors in plants to defend against caterpillars, butterflies and other pests. Brassicales species first evolved glucosinolate defenses around the KT Boundary — when dinosaurs went extinct — and eventually diversified to synthesize more than 120 different types of this compound.

For most insects, these glucosinolates prove toxic, but certain ones like the cabbage butterfly evolved ways to detoxify the compounds.

“Seeing the variation in the detoxification mechanisms among species and their gene copies gave us important evolutionary insights,” said Hanna Heidel-Fischer, a lead author on the study based at the Max Plank Institute for Chemical Ecology in Germany.

To look at these genetic differences, the team used 9 existing Brassicales genomes and also generated transcriptomes — the set of all RNA in a cell — across 14 Brassicales families. This allowed the team to map an evolutionary family tree of sorts over the millennia, seeing where major defense changes occurred. This family tree was compared with the family tree of 9 key species of Pieridae butterflies, which includes the cabbage butterfly.

Pires and his colleagues identified three significant evolutionary waves over 80 million years, where plants developed defenses and insects evolved counter tactics.

Pat Edger | Image by Roger Meissen, Bond LSC

Pat Edger | Image by Roger Meissen, Bond LSC

“We found that the origin of brand-new chemicals in the plant arose through gene duplications that encode novel functions rather than single mutations,” said Pat Edger, a former MU post doc and lead author on the study. “Given sufficient amounts of time the insects repeatedly developed counter defenses and adaptations to these new plant defenses.”

This back-and-forth pressure resulted in the evolution of many more species of plants and butterflies than in other groups without glucosinolate pressures.

Proving an old concept

Co-evolution is not a new idea.

About 50 years ago two now-renowned biologists, Peter Raven and Paul Erhlich, introduced the idea of co-evolution to science. Using cabbage butterflies and Brassica plants as a prime example, the two published a landmark study in 1964 advancing the idea that two species can mutually influence the development and evolution of each other.

To explore the genetics of how this works, Pires’ lab partnered with Chris Wheat, professor of population genetics in the Department of Zoology at Stockholm University.

“Using Ehrlich and Raven’s principles and models, we looked at the evolutionary histories of these plants and butterflies side-by-side and discovered that major advances in the chemical defenses of the plants were followed by butterflies evolving counter-tactics that allowed them to keep eating these plants,” Wheat said.

Chris Pires and colleagues mapped the evolution of Brassicales and butterflies to find how each evolved to combat the defenses of the other. | Courtesy Chris Pires

Chris Pires and colleagues mapped the evolution of Brassicales and butterflies to find how each evolved to combat the defenses of the other. | Courtesy Chris Pires

This research provides striking support for the ideas of Ehrlich and Raven published 50 years ago.

“We looked at the patterns 50 years ago, and found conclusions that proved correct,” said Peter Raven, professor emeritus of the Missouri Botanical Garden and a former University of Missouri Curator. “The wonderful array of molecular and other analytical tools applied now under leadership of people like Chris Pires, provide verification and new insights that couldn’t even have been imagined then.”

Understanding more about how plants and insects co-evolve could one day lead to advances in crops.

“If we can harness the power of genetics and determine what causes these copies of genes, we could produce plants that are more pest-resistant to insects that are co-evolving with them—it could open different avenues for creating plants and food that are more efficiently grown,” said Pires.

Proceedings of the National Academy of Sciences (PNAS) published the study, “The butterfly plant arms-race escalated by gene and genome duplications,” in June. The National Science Foundation (PGRP 1202793), the Knut and Alice Wallenberg Foundation and the Academy of Finland provided the funding for this research.

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.