plant sciences

Walter Gassmann #IAmScience

Walter Gassmann

Walter Gassmann, the new Interim Director of Bond LSC. | Photo by Roger Meissen, Bond LSC

By Mary Jane Rogers | Bond LSC

“#IAmScience because science is the best way to solve problems and help people. And the laws of nature write fascinating stories.”

Walter Gassmann, the new Interim Director of Bond LSC, has been an important part of the MU science community for more than a decade. He’s a member of the Interdisciplinary Plant Group, a researcher in Bond LSC and a professor in the Division of Plant Sciences within the College of Agriculture, Food and Natural Resources.

His research deals with how plants fight diseases and he specifically investigates the inner workings of plants’ immune systems, which are highly specialized in detecting the presence of foreign and potentially harmful organisms. Apart from figuring out how this detection works, Gassmann is interested in finding mechanisms that plants use to keep their immune system in check. The plant immune response is very potent in stopping pathogen spread, but if left unchecked it has the tendency to harm the surrounding plant tissue as well.

Fundamental plant pathology research, what Gassmann’s work deals with, has contributed to many agricultural gains, and will continue to provide avenues for improved crop yields. It has also led to many new insights for biology in general. For example, the concept of a virus was first developed in the late 1800s with work on tobacco mosaic virus. The tit-for-tat between plants and their pathogens has shaped plant immune systems and pathogen countermeasures for eons, and also affords a fascinating glimpse into the processes that shape the evolution of complex organisms.

In recognition of his outstanding contributions to plant pathology, Gassmann was elected as a Fellow of the American Association for the Advancement of Science in 2016.

We look forward to your leadership, Dr. Gassmann!

The evolution of a corn geneticist

By Jennifer Lu |Bond LSC

Paula McSteen

Bond LSC Biologist Paula McSteen | photo by Jennifer Lu, Bond LSC

When developmental plant geneticist Paula McSteen thinks about the specimens she studies, one word comes to mind: potential.

She thought it as she stood in the midst of the first corn field she ever planted as a post-doctoral fellow in corn genetics.

She thinks it as she counts kernels from corn crosses that will be sent to Hawaii, a hotspot for corn geneticists looking to add a second harvest to their research year.

And she sees it in the students she mentors as a professor of biological sciences at MU and a researcher at the Bond Life Sciences Center.

Embracing the corn

McSteen entered the field of corn genetics 21 years ago, as a post-doctoral fellow in Berkeley.

“What’s really amazing is that when you plant a field of corn, the field is just bare,” McSteen says.

“A few weeks later, you come back and your plants are this high,” she says, gesturing with her hands. “And a few weeks later, they’re this high. And a few weeks later, they’re massive and it’s all just coming from nothing. The instructions are there in the seeds, but otherwise the plant is taking nutrients and water from the soil and using the air and sun to generate sugar for growing. It’s amazing. You come back and you’ve got this whole field of corn.”

During her first corn season, McSteen remembers being surrounded as far as the eye can see by corn as tall as people. “I feel like that’s one reason why people get into corn. You’re not staring down into a microscope, you’re embracing it. It’s right there in front of you.”

The feeling hasn’t gone away.

“When I see my plants,” McSteen says, “I’m excited about what’s going on with them. What could be happening here? What’s the meaning of these results?”

McSteen, who is Irish, grew up far removed from the sunny cornfields she works in. As a child in Dublin, she wasn’t particular outdoorsy. When her family went camping by the sea over the summer holidays, McSteen spent most of her time reading books. Her favorite subject in school was science. By the time she sat for her high school leaving exam, her classes were mainly in geography, science or math.

“I’ve always been fascinated with genetics,” McSteen says. Ever since she learned about Punnett squares in high school, its puzzle-like quality has appealed to her. “I just loved that you could figure out what the prediction could be from a certain cross.”

She applied and was accepted to her top choice university, Trinity College Dublin, where she studied genetics. She went on to pursue a PhD in Norwich, England studying how snapdragons make flowers.

When it came time for her to do her post-doc, she had the choice to work on Arabidopsis, a popular plant model, or maize, a crop with many opportunities for research funding. She chose the latter. The decision changed the course of her career, from her research focus to her country of residence.

Corn brought her to California, Pennsylvania and then the University of Missouri, which has a long history of corn genetics.

Pollen

Researchers cross-pollinate corn by pouring pollen collected from the tassel over the ear. | Photograph by Jennifer Lu, Bond LSC

Everything we do starts with mutants

McSteen studies a part of corn plants called the meristem, which is filled with stem cells that become the reproductive organs of the plant: the tassel and the ears.

The tassel, where pollen is produced, is found at the top of the cornstalk, while the ears, which are the female reproductive organs, jut out from the sides. When and how they form depend on a growth hormone called auxin.

To understand auxin regulation, McSteen begins every summer with a field full of mutants. Each kernel contains a mutation, but it’s impossible to tell at first what is causing the mutation.

“To me, every single mutant is just potential. You can’t wait to find out what is mutated. You never know what you’re going to end up with.”

McSteen is interested in mutations that affect the tassels or ears. These plants produce ears with fewer kernels or tassels with fewer branches. Or they fail to make ears or tassels altogether. The defects are outward signs of problems in meristem development, and hint at disruptions to genes that are involved in how auxin is made, transported or perceived by the plant.

Once a mutant is identified, McSteen works backwards to find out which gene is causing the mutation, and where it is located on the chromosome. To date, her group has identified multiple genes related to auxin-mediated development, as well as two genes that affect the uptake or synthesis of essential nutrients.

A third project revolves around a strain of corn that produces half as many kernels as regular corn, causing it to look like grains such as rice or wheat. McSteen thinks that if they can understand what’s causing the shortfall in kernel development, it may be possible to engineer grains like rice and wheat to “double kernel” the way that corn does.

Ultimately, studying these genes help corn researchers to better understand plant development and improve yield.

Eden Johnson

Graduate student Eden Johnson photographs a mutant that has produced half as many rows of kernels. | Photograph by Jennifer Lu, Bond LSC

You always love the organism

To keep all their experiments going, the McSteen lab plants three acres of corn every summer. Each acre contains 750 rows; each row holds 30 plants.

With the aid of a hand held planter, they drop 67,500 kernels into the soil. Then they do what McSteen calls a lopsided “planter’s shuffle” to stamp the soil down so that it covers every kernel.

“You can do a whole acre of corn in a few hours,” she said. “It’s hard work. You’re sore afterwards.”

During Missouri summers, temperatures can reach over 100 degrees Fahrenheit. It feels even hotter when it rains. The ground is either hard as a rock before it rains or so muddy after it rains that researchers have to take care not to wrench their ankles in the thick muck.

McSteen has worked on corn for so long that she’s developed severe allergies to corn pollen. It’s not uncommon among corn researchers, but her allergies prevent her from taking part in the pollination step that takes place at the height of summer.

“You’re out there in 100-degree heat getting the job done,” she says. “It’s a real bonding experience for the lab.”

To pollinate the corn, they slip paper bags over the ears and tassel of their plants. Covering the ears prevents accidental fertilization of the ears from stray pollen blown about by the wind. The bag over the tassel allows researchers to collect the yellow powder that will be used for controlled pollination.

“The next day, you bang the tassel and the pollen falls out into the bag,” McSteen says. “Then you gather it all up and you pour it on the ear.” It’s possible to pollinate about 100 plants in an hour, but you have to start early and work quickly, McSteen says. Otherwise, all the pollen is dead by noon.

McSteen’s allergies prevent her from shelling corn as well, but she’s on deck for planting and harvest time and all the other stages in between.

“If you’re a corn geneticist, you’re out there working with the plants. You always love the organism.”

Paula McSteen

Paula McSteen labels the envelope of kernels from a corn cross that will be grown in Hawaii. | Photograph by Jennifer Lu, Bond LSC

A Collaborative Community

“To be a corn geneticist, you have to be very organized and plan ahead,” McSteen says. Because it takes a long time to grow several generations of corn, she’s only beginning to see the results of experiments she started years ago.

As a way to increase productivity, corn researchers send their seeds to warm places such as Mexico, Chile or Hawaii that can accommodate a winter harvest.

In the lab, McSteen chooses kernels from carefully selected mutants to ship to an island in Hawaii. There, a company will plant and harvest the corn for her, but she usually sends two of her researchers down to take care of the pollinations themselves.

McSteen counts out thirteen yellow kernels that are shiny and mold-free. “Potential,” she says, as she slips the seeds in an envelope with the cross information labeled on the front.

A three week trip to Hawaii in the winter isn’t as exotic as it sounds, says Eden Johnson, a third year graduate student in McSteen’s lab. On the island, the beaches are rocky and full of riptides. “It is literally cornfields, one diner and a stop sign. The whole island exists for corn.”

“When you’re down there in Hawaii, you hang out with the other researchers,” McSteen says. “If their field is peaking and your field is not, then you’ll go help.”

In her experience, the corn community tends to be collaborative rather than competitive. She suspects it’s because everyone recognizes that corn takes a long time to grow.

“If you find out you’re working on similar things, you’ll work together, divide the work and do it together,” McSteen says. Researchers don’t race each other to be the first one to publish. “They won’t do that because they have respect for how long it takes to grow the corn.”

Katy Gurthrie

Katy Gurthrie removes a bag used to collect pollen from the tassel. | Photograph by Jennifer Lu, Bond LSC

Growing careers alongside corn

McSteen is as serious about mentorship as she is about corn. “It’s part of the job of being a professor”.

According to Katy Guthrie, a second year graduate student in the lab, McSteen takes a Goldilocks approach to managing her students.

Neither too hands on or too hands off, “it’s exactly what I need,” Guthrie says. “She’s kind of like my academic parent for the next five years.”

Back at Penn State, McSteen supervised a PhD student who was talented writer. “I noticed this and gave her opportunities to write.” McSteen introduced her to a science writer and encouraged her to spend a summer writing for a science publication. “Now she works for the National Academy of Sciences. I’m really proud of her, and I feel like she’ll have a big impact communicating science to the public.”

A post-doc wanted to do go into teaching, so McSteen invited her to co-teach her class. Her post-doc went on to become a teaching professor at Mizzou. Another student turned her research experience in mapping mutants in corn into a successful career at a corn company.

“I want to enable the people in my lab to reach their full potential,” McSteen says. “I always try to figure out what they want to do in the future and try and facilitate that.”

 

Planting a seed for sciences

Rhizobia bacteria

Plants on the left grow with rhizobia bacteria, one type of fixing nitrogen bacteria, in the greenhouse, while the plants on the right grow without the bacteria. | photo by Jinghong Chen, Bond LSC

Jinghong Chen | Bond Life Sciences Center

Since eight years old, Beverly Agtuca knew she wanted to be a scientist.

A trip to Philippines changed Agtuca, an American-born Filipino, and inspired her passion on plants.

“My grandma always told me to work in the field all day so that they can have enough food for us to eat,” Agtuca said. “The life [in Philippines] is so different from here…I want to not just provide food but be that scientist trying to figuring something out, and hopefully saving the world.”

Agtuca is on her way to her dream. She is now a third year doctoral student in Gary Stacey’s lab at Bond Life Sciences Center with a focus on nitrogen-fixing bacteria.

Although she has been involved in research since high school, Agtuca recently faced a new challenge of telling people about her work. The Preparing Tomorrow’s Leaders of Science class tasked her with making a 90-second video to explain her two-year study to the general public.

Her team, “The A Team,” chose to go with the benefits of having nitrogen-fixing bacteria.

For decades, people have been adding nitrogen fertilizers to plants to improve yields, but this can lead to pollution in water systems and ecosystems. Scientists need to enhance plant productivity to meet a huge food demand by the year of 2050.

One little bacteria might make this possible and save the world. Rhizobia, a type of natural bacteria in soil, are able to fix nitrogen via biological nitrogen fixation. These bacteria can convert nitrogen gas into ammonia as a plant nutrient source, while the plants give all the carbon sources back to the bacteria.

“It is like a walky-talky,” Agtuca said. “They are communicating with each other.”

Yet before speaking to the public, Agtuca needs to explain the plant-bacteria interaction to her teammates. Students less well versed in science like Jessica Kaiser, a strategic communication student, thinks of science differently.

“The biggest issue we ran into is jargon, like basic science words that [my teammates] are so comfortable with,” Kaiser said. “We need to focus on what people care about instead of the technical sides, to focus on why it matters to anybody rather than just to a science person.”

Within two weeks, they produced the video “Good Microbes: reducing pollution one farm at a time.” Along with two other teams, their videos will be commented and judged by representatives from Monsanto.

"The A Team"

“The A Team” stands together at Bond Life Sciences Center. From left to right: Jessica Kaiser, Sven Nelson, Anna Glowinski, Eleni Galata and Beverly Agtuca. | photo by Jinghong Chen, Bond LSC

The 90-second video is just a glimpse of Agtuca’s study. In the last two years she has been focusing on the use of a new technique — laser ablation electrospray ionization mass spectrometry (LAESI-MS) — that does in situ metabolic profiling of tissues. The lab is using LAESI-MS to investigate the metabolites in a well-characterized model plant-rhizobium system, specifically nitrogen-fixing soybean nodules resulting from root infection by the symbiotic bacterium Bradyrhizobium japonicum.

This work includes a huge collaboration that was developed through a Department of Energy (DOE) grant involving the George Washington University, Washington D.C. and the Environmental Molecular Science Laboratory (EMSL), Pacific Northwest National Laboratory, Richland, WA.

LAESI-MS works like a superhero’s laser-like beams. You first aim the laser on the sample, which then heats it and causes neutral particles to be released into the air. This plume of neutrals is then captured and ionized by the electrospray, and finally analyzed by the spectrometer to figure out the exactly what metabolites in nodules are involved in biological nitrogen fixation.

“It takes about three seconds to analyze one sample using this LAESI-MS technique,” Agtuca said. Other metabolic techniques require extensive pre-treatment of the sample before analysis.

By analyzing the data collected via LAESI-MS, the lab is able to confirm that future plant studies could apply this new approach to understand the interactions between plant and bacteria.

Agtuca’s research is a long way from her first experiences with plants. She still remembers the moment she found her plants in her own garden died. She was less than 10 years old, yet devoted to taking care of her plants with water and fertilizers.

“I was really sad. I could not get my tomatoes, peppers and eggplants to live.…That makes me think that I want to answer why they didn’t grow,” Agtuca said.

More than ever, her future is helping her answer those question for herself.

 

Gary Stacey is a Bond LSC investigator and MU curators’ professor of plant science and MSMC endowed professor of soybean biotechnology. Read more here about Stacey lab.

Sven Nelson is a USDA/ARS postdoctoral research scientist at the University of Missouri. Anna Glowinski is a Ph.D. student in the USDA/ARS lab. Jessica Kaiser is a graduate student in strategic communication. Eleni Galata works as the team mentor and she is a Ph.D. student in agricultural and applied economics at MU.

Understanding spit

Scientists find how nematodes use key hormones to take over root cells

Roger Meissen | Bond Life Sciences Center
This Arabidopsis root shows how the beet cyst nematode activates cytokinin signaling in syncytium 10 days after infection. The root fluoresces green when the TCSn gene associated with cytokinin activation is turned on because it is fused with a jellyfish protein that acts as a reporter signal. (N=nematode; S=Syncytium). Contributed by Carola De La Torre

This Arabidopsis root shows how the beet cyst nematode activates cytokinin signaling in the syncytium 10 days after infection. The root fluoresces green when the TCSn gene associated with cytokinin activation is turned on because it is fused with a jellyfish protein that acts as a reporter signal. (N=nematode; S=Syncytium). Contributed by Carola De La Torre

This is a story about spit.

Not just any spit, but the saliva of cyst nematodes, a parasite that literally sucks away billions in profits from soybean and other crops every year.

Researchers are working to uncover exactly how these tiny worms trick plant root cells into feeding them for life.

A team at the University of Missouri Bond Life Sciences Center collaborated with scientists at the University of Bonn in Germany to discover genetic evidence that the parasite uses its own version of a key plant hormone and that of the plants to make root cells vulnerable to feeding. Their research recently appeared in Proceedings of the National Academy of Sciences.

Melissa Mitchum

Melissa Mitchum

Cytokinin is normally produced in plants, but these researchers determined that this growth hormone is also produced by nematode parasites that use it to take over plant root cells.

“While it’s well-known that certain bacteria and some fungi can produce and secrete cytokinin to cause disease, it’s not normal for an animal to do this,” said Melissa Mitchum, an MU plant scientist and co-author on the study. “This is the first study to demonstrate the ability of an animal to synthesize and secrete cytokinin for parasitism.”

 

 

Not Science Fiction

Reprogramming another organism might sound like a far out concept, but it’s a reality for plants susceptible to nematodes.

Cyst nematodes hatch from eggs laid in fields and quickly migrate to the roots of nearby plants. They inject nematode spit into a single host cell of soybean, beet and other crop roots.

Carola De La Torre

Carola De La Torre

“Imagine a hollow needle at the head of the nematode that the parasite uses to penetrate into the plant cell wall and secrete pathogenic proteins and hormone mimics,” said Carola De La Torre, a co-author of the study and plant sciences PhD student with Mitchum’s lab. “Nematodes use the spit to transform the host cell into a nutrient sink from which they feed on during their entire life cycle. This de novo differentiation process greatly depends on nematode–derived plant hormone mimics or manipulation of plant hormonal pathways caused by effector proteins present in the nematode spit.”

These effector proteins and other small molecules in their spit cause the root cell to forego normal processes and create a huge feeding site called a syncytium. In a short period of time, this causes hundreds of root cells to combine into a large nutrient storage unit that the nematode feeds from for its entire life.

Being able to convince a root cell to do the nematode’s bidding starts with a takeover of the plant host cell cycle — which regulates DNA replication and division. This implies that a plant hormone like cytokinin is involved, says Mitchum. Cytokinin normally regulates a plant’s shoot growth, leaf aging, and other cell processes.

 

Proving the relationship

While Mitchum’s lab had a hunch that cytokinin was key to this takeover, proving it took some creative science.

De La Torre and Demosthenis Chronis, a postdoctoral fellow MU at the Bond LSC depended on mutant Arabidopsis plants to explore the relationship. “One of the great things about using Arabidopsis as our host plant is the vast genetic resources of cytokinin and hormone mutants that are available through the scientific community,” De La Torre said.

She infected Arabidopsis that contained a reporter gene called TCSn/GFP with nematodes. This gene is associated with cytokinin responses within the plant cells and is fused with a jellyfish protein that glows green when turned on. So, De La Torre saw nematodes activated cytokinin responses in the plant early after infection when her plants emitted a green fluorescent glow under the microscope.

Next, she infected plants missing the majority of their cytokinin receptors with nematodes. Then she started counting nematodes present.

“After a careful evaluation of nematode infection, we observed less female nematodes developing in the receptor mutants compared to the wild type” De La Torre said. “The nematodes could not infect well, and that was a clear piece of evidence suggesting that cytokinin plays a main role in plant–nematode interactions.”

Another experiment looked at Arabidopsis containing a reporter gene called GUS that was fused to the regulatory sequences of the cytokinin receptor genes. All three cytokinin receptor genes were activated where the nematode was feeding.

A final experiment used a mutant that created an excess of an enzyme that degrades cytokinin, finding that a base level of plant cytokinin was also necessary for nematode growth.

“The simple statement is that the cytokinin receptors were activated in response to nematode infection and the mutants did not support growth and development of the nematodes,” Mitchum said. “This shows that if you take away the ability of the plant to recognize cytokinin the worms are unable to fully develop.”

 

An international collaboration

Mitchum’s team did not work alone.

The lab of Florian Grundler at Rheinische Friedrich-Wilhelms-University of Bonn, Germany, was also on a mission to uncover if genes in the nematode controlled cytokinin activation. They had identified a key gene in the beet cyst nematode that makes the cytokinin hormone. When they took away the ability of the nematode to secrete cytokinin certain cell cycle genes were not activated at the feeding site and the nematodes did not develop. Now we know that the nematode is also secreting cytokinin to modulate the pathways.

De La Torre took that information and found the same gene in the soybean cyst nematode.

Now, Mitchum’s team is trying to find how this key gene might work differently in other nematode types, like root-knot nematode as part of a new National Science Foundation grant. They hope this will help lead to better resistance in future crops.

“Understanding how the nematode modulates its host is going to help us exploit new technologies to engineer plants with enhanced resistance to this terribly devastating pathogen,” Mitchum said. “Technology is changing all the time, we’re gaining new tools constantly, so you never know when something new is going to allow us to do something specific at the site of nematode feeding that will lead to a breakthrough.”

Mitchum is a Bond LSC investigator and an associate professor of Plant Sciences in the College of Agriculture, Food and Natural Resources. The study “A Plant Parasitic Nematode Releases Cytokinin that Control Cell Division and Orchestrate Feeding-Site Formation in Host Plants” recently was published by the Proceedings of the National Academy of Sciences and was supported by the National Science Foundation (Grant #IOS-1456047 to Mitchum). The content is solely the responsibility of the authors and does not necessarily represent the official views of the funding agencies.

Frogs help researchers find genetic mechanism for mildew susceptibility in grapevine

Powdery mildew on a cabernet sauvignon grapevine leaf. | USDA Grape genetics publications and research

Powdery mildew on a cabernet sauvignon grapevine leaf. | USDA Grape genetics publications and research

A princess kisses a frog and it turns into a prince, but when a scientist uses a frog to find out more information about a grapevine disease, it turns into the perfect tool narrowing in on the cause of crop loss of Vitis vinifera, the world’s favorite connoisseur wine-producing varietal.

MU researchers recently published a study that uncovered a specific gene in the Vitis vinifera varietal Cabernet Sauvingon, that contributes to its susceptibility to a widespread plant disease, powdery mildew. They studied the biological role of the gene by “incubating” it in unfertilized frog eggs.

The study, funded by USDA National Institute of Food and Agriculture grants, was lead by Walter Gassmann, an investigator at the Bond Life Sciences Center and University of Missouri professor in the division of plant sciences.

The findings show one way that Vitis vinifera is genetically unable to combat the pathogen that causes powdery mildew.

Gassmann said isolating the genes that determine susceptibility could lead to developing immunities for different varietals and other crop plants and contribute to general scientific knowledge of grapevine, which has not been studied on the molecular level to the extent of many other plants.

The grapevine genome is largely unknown.

“Not much is known about the way grapevine supports the growth of the powdery mildew disease, but what we’ve provided is a reasonable hypothesis for what’s going on here and why Cabernet Sauvingon could be susceptible to this pathogen,” Gassmann said.

The research opens the door for discussion on genetically modifying grapevine varietals.

Theoretically, Gassmann said, the grapevine could be modified to prevent susceptibility and would keep the character of the wine intact — a benefit of genetic modification over crossbreeding, which increases immunity over a lengthy process but can diminish character and affect taste of the wine.

Grapevine under attack

Gassmann’s recent research found a link between nitrate transporters and susceptibility through a genetic process going on in grapevine infected with the powdery mildew disease.

Infected grapevine expressed an upregulation of a gene that encodes a nitrate transporter, a protein that regulates the makes it possible for the protein to enter the plant cell.

Once the pathogen is attracted to this varietal of grapevine, it tricks grapevine into providing nutrients, allowing the mildew to grow and devastate the plant.

As leaves mature, they go through a transition where they’re no longer taking a lot of nutrients for themselves. Instead, they become “sources” and send nutrients to new “sink” leaves and tissues. The exchange enables plants to grow.

The powdery mildew pathogen, which requires a living host, tricks the grapevine into using its nutrient transfer against itself. Leaves turn into a “sink” for the pathogens, and nutrients that would have gone to new leaves, go instead, to the pathogen, Gassmann said.

“We think that what this fungus has to do is make this leaf a sink for nitrate so that nitrate goes to the pathogen instead of going to the rest of the plant,” Gassmann said.

Walter Gassmann, of the Bond Life Sciences Center at the University of Missouri was the lead investogator on the research. Much of his work has been on grapevine susceptibility to pathogens.

Walter Gassmann, of the Bond Life Sciences Center at the University of Missouri was the lead investogator on the research. Much of his work has been on grapevine susceptibility to pathogens. | Roger Meissen, Bond Life Sciences Center

According to a report by the USDA, powdery mildew can cause “major yield losses if infection occurs early in the crop cycle and conditions remain favorable for development.”

Powdery mildew appears as white to pale gray “fuzzy” blotches on the upper surfaces of leaves and thrives in “cool, humid and semiarid areas,” according to the report.

Gassmann said powdery mildew affects grapevine leaves, stems and berries and contributes to significant crop loss of the Vitas vinifera, which is cultivated for most commercial wine varietals.

“The leaves that are attacked lose their chlorophyll and they can’t produce much sugar,” Gassmann said. “Plus the grape berries get infected directly, so quality and yield are reduced in multiple ways.”

Pinpointing a cause

Solutions to problems start with finding the reason why something is happening, so Gassmann and his team looked at a list of genes activated by the pathogen to find transporters that allowed compounds like peptides, amino acids, and nitrate to pass.

Genes for nitrate transporters, Gassmann said, pointed to a cause for vulnerability to the mildew pathogen.

Over-fertilization of nitrate increases the severity of mildew in many crop plants, according to previous studies sited in Gassmann’s article in the journal of Plant Cell Physiology.

The testing system for isolating and analyzing the genes began with female frogs.

Gassmann used frog oocytes (unfertilized eggs), to verify the similar functions of nitrate transporters in Arabidopsis thaliana, a plant used as a baseline for comparison.

A nitrate transporter, he hypothesized, would increase the grapevine’s susceptibility to mildew.

“The genes that were upregulated in grapevine showed similarity to genes in Arabidopsis that are known to transport nitrate,” Gassmann said. “We felt the first thing we had to do was verify that what we have in grapevine actually does that.”

The eggs are very large relative to other testing systems and act as “an incubating system” for developing a protein. Gassmann and his team of researchers injected the oocyte with RNA, a messenger molecule that contains the information from a gene to produce a protein. The egg thinks it’s being fertilized and protein reproduces and is studied.

“The oocyte is like a machine to crank out protein,” Gassmann said. “We use that technique to establish what we have is actually a nitrate transporter.”

The system confirmed that the gene isolated from grapevine encodes a nitrate transporter.

“We contributed to the general knowledge of the nitrate transporter family,” Gassmann said. “It turned out to be the first member of one branch of nitrate transporters that, even in Arabidopsis haven’t been characterized before.”

The mounting knowledge of Vitis vinifera genes could make genetically modifying the strain to prevent the susceptibility easier.

“Resistance is determined sometimes by a single gene,” Gassmann said. “Until people are willing to have the conversation of genetic modification, the only way to save your grapevines is to be spraying a lot.”

Sharon Pike, Gassmann, other investigators from the MU Christopher S. Bond Life Sciences Center and post-doctoral student, Min Jung Kim from Daniel Schachtman’s lab at the Donald Danforth Plant Science Center in Saint Louis, Mo. contributed to the report.

The article was accepted November 2013 into the Plant Cell Physiology journal.