It might not sound like a traditional undergraduate experience, but Elizabeth Prenger and Andrew Ludwig found success studying a tiny parasitic worm.
It’s called the soybean cyst nematode (SCN) and it sucks more than a billion dollars a year from American soybean farmers. While farmers have used resistant soybeans and crop rotation to fight against the pest, the nematodes continue to gain ground against increasingly less effective methods to control them.
Working in the lab of Melissa Mitchum, a Professor of Plant Sciences at MU’s Bond Life Science Center, they helped understand how soybeans naturally resist this worm and how SCN evades these protections.
That work recently paid off as they saw their names published in the journal Plant Physiology in November 2017. The study explored the genetic mechanisms behind resistance in order to develop better prevention.
“If scientists can understand how resistance genes work and interact then that information can be applied in breeding and developing soybeans,” said former Mitchum lab member Elizabeth Prenger.
While the findings were published in 2017, for Prenger and Andrew Ludwig the research began several years ago.
Prenger came to college knowing she wanted to improve crops and help farmers like her family, she just wasn’t sure exactly how. She joined Mitchum’s lab as a freshman to begin to find out.
As a freshman and sophomore, Prenger worked to purify, sequence and analyze DNA of various soybeans to help further characterize the SHMT gene, a gene that plays a role in a plant’s ability to resist the pest. She also worked in the greenhouse to identify soybeans with mutations in this gene by infecting them with SCN.
Her fellowship supported by the MU Monsanto Undergraduate Research Program sparked her interest in plant genetics but she also realized she wanted more interaction with plants beyond the lab.
Without this early immersion into the lab, Prenger said it would have taken her longer to find her interests.
Now, as a graduate student, she studies soybean genetics at the University of Georgia.
Ludwig’s position in the lab helped him find his direction in science as well.
He applied for a position while still in high school through the MU Honors College Discovery Fellows Program. The fellowship funds and places undergraduates in labs across campus. His interest in the genetic modification of crops led him to the Mitchum lab.
For three years, Ludwig helped infect different mutants with the nematode and then compare the effect on resistance. This screening helped narrow down the genetic possibilities controlling soybean resistance to a single gene.
“We were hoping the soybeans would have a mutation in one of the resistance genes and then that mutation would cause the gene to cease function so you would see a lot of nematodes on a plant that shouldn’t have any,” he explained.
This experience taught Ludwig how to think like a scientist by developing problem-solving skills.
“I think working in the lab was an immensely valuable experience because I learned so much about what it is to be a scientist and it opened my eyes to a lot more of what the field of plant science really is,” he said.
It also taught him that a traditional lab work environment was not for him. As Ludwig begins to apply for graduate school he is planning to major in horticulture.
His goals changed from wanting to create GMO crops for other countries to now hoping to solve food insecurity closer to home by working with sustainable agriculture and food deserts.
Since joining Mitchum’s lab as undergraduates, both Prenger and Ludwig learned what it means to be scientists and shaped where they are today. The publication of the research that started the path to where they are today was a satisfying conclusion.
“It’s really rewarding to see that all the work exists outside of my lab notebook now,” Ludwig said.
Reflecting on their experience, both students urged other undergraduates to get in a lab as soon as they can to begin discovering themselves and science.
“Go for it. It’s a really helpful experience, it will make you better at what you do even if what you end up doing is different from what you thought you’d do,” Ludwig recommended.
Scientific success largely hinges on research results, and four recent promotions at Bond Life Sciences Center celebrate that achievement.
Cheryl Rosenfeld, D Cornelison and Melissa Mitchum of Bond Life Sciences Center were promoted to full professor as of September 1, while Laurie Erb received a promotion as a non-tenure-track research professor. They are the first female full professors in Bond LSC’s 13-year history.
University of Missouri’s Assistant Vice Chancellor of the Division of Inclusion, Diversity and Equity, Noor Azizan-Gardner, said the promotions made her optimistic.
“Three women all going up to full professor – it’s phenomenal,” she said. “And the fact that they all have labs in Bond LSC makes me deliriously happy. Not just for us and them, but for the women who will be the next generation. The ripple effect is bigger than just the three of them.”
Promotion and tenure at MU follows rigorous guidelines that take teaching, research success and service into account to advance professors through three tiers — from assistant to associate to full professorship — over more than a decade.
But like many technical fields, science lags behind in its proportion of women to men. Growing that diversity is important to the breadth of scientific inquiry. As an advocate of collaboration, the promotion of three women to full professor at Bond LSC hopes to reinforce that diversity.
Cornelison and Mitchum were quick to stress their promotions had nothing to do with their gender, and everything to do with their science.
“It just doesn’t cross my mind,” Mitchum said. “I honestly don’t walk around thinking about gender. I just do the best I can and that’s all I can do.”
Similarly, Cornelison said, “I am not a female scientist. I am a scientist. Period. It should not be a part of the story.”
Rosenfeld, however, is concerned that administrators are not giving women the support necessary to flourish in their careers.
“I work seven days a week and I deserve respect and to be taken seriously on par with my male colleagues,” she said. “I am not doing this as a hobby. This is my passion, and, hopefully in the future, women like myself will be treated equally.”
A Pervasive Problem
A study conducted in 2015 by the Chancellor’s Status of Women Committee and the Status of Women Committee in the College of Arts and Science at MU found that with regard to gender equity on campus, there was no evidence of a systematic pay bias against female faculty. However, it did find that the average salary for female faculty is almost $16,000 (or 15 percent) below the average salary for male faculty and that the colleges with the highest average salaries were predominantly male.
Cornelison, Mitchum and Rosenfeld all believe that female scientists at MU face at least three significant hurdles on their path to full professor: the amount of time it takes compared to their male colleagues, the lack of mentorship, and the high ratio of male full professors compared to female full professors in several departments.
Mitchum stated that there are only two other female full professors — Jeanne Mihail and Michelle Warmund — in the plant sciences department compared to at least 17 males. Rosenfeld and Cornelison had similar ratios in their respective departments.
Recent controversies indicate gender equity is a persistent challenge in the field as a whole.
In 2015, a study published by the American Psychological Association found that when considering requests from prospective students seeking mentoring in the future, the science faculty at research-intensive universities were more likely to hire a male lab manager, mentor him, pay him more and rate him as more competent than a female candidate with the exact same resume. And this year, two senior female scientists sued the prestigious Salk Institute for Biological Studies, alleging pervasive gender discrimination and systematic sexism.
Although female scientists remain underrepresented in many countries, academic journal publisher Elsevier released a report in 2017 that shows improvement. It stated that women’s scholarly authorship increased overall from 30 percent in the late 1990s to 40 percent two decades later. In terms of raw proportions, the percentage of women scientists in the U.S. increased from 31 percent from 1996-2000 to 40 percent from 2011-2015.
Rosenfeld, Cornelison and Mitchum’s success in the departments of Biomedical Sciences, Biological Sciences and Plant Sciences, respectively, follow several decades of hard work and passion in their fields.
But their interest in science started in unique ways.
“In middle and high school I was always excited about science classes,” said Mitchum. “I liked physics. I liked chemistry. I was lucky to have a science teacher, Patty Gustin, who knew I had an interest in science, saw some potential and encouraged me. She was actually the first person to encourage me to go on to college in science.”
Mitchum went on to get an undergraduate degree in biology at the University of Puget Sound in Tacoma, Washington. She immediately continued her education and received her masters in plant pathology at the University of Nebraska, Lincoln and her Ph.D. in plant pathology and biotechnology at North Carolina State University in Raleigh.
Cheryl Rosenfeld’s high school biology teacher, Patricia Murphy, was also the first person to put her on the science track.
“I can still picture her to this day,” Rosenfeld said, smiling. “She gave me a C on my first lab assignment. My friend received a better grade and we did the same work, so I asked her why I got such a low grade. She told me that I was going to be a scientist, that she expected more of me, and to improve my grade she allowed me to help prep the lab experiments.”
Rosenfeld went on to receive a bachelor of science and DVM (Doctor of Veterinary Medicine) from the University of Illinois at Urbana-Champaign and a Ph.D. in Animal Sciences and Reproductive Biology from MU.
Cornelison’s path was a bit different. Like many undergraduate scientists, she initially thought she would go to medical school. But during an independent study, she was assigned to a lab doing behavior genetics in mice and fell in love with research.
“Unlike my experience in Chemistry classes, I was now in an environment where I was expected to go and do things nobody had ever done before,” Cornelison said. “And I got to tell people about it. And I got to decide what the next unknown thing I wanted to know was. After that, I had to decide whether to apply to medical school or graduate school because I only had enough money to take the GRE or the MCAT, so I took the GRE. And I am still incredibly grateful for the people who took me into their lab and taught me to science.”
Cornelison credits that experience with why she enjoys having undergraduates in her lab. To date, over 20 of them have graduated with departmental honors based on their independent research projects.
“If I can give students a taste of what that experience of discovery feels like, I’m happy. It changes your perspective on many things,” she said.
The concept of mentorship is something Rosenfeld, Cornelison and Mitchum all agree is critical for budding scientists, male or female.
Each shared stories about the vast amount of mentors that inspired them and students they still keep in contact with. Mitchum has an especially meaningful relationship with one of her mentors.
“While I was working in a lab as an undergraduate I had the opportunity to interact with a visiting scientist who would work in our lab, Donald Foard, an older gentleman at the time, and he became my mentor,” Mitchum said fondly. “I don’t think I would be where I am today without his mentorship. As an undergraduate, he encouraged me. He believed in me. He inspired me to go to graduate school. And we still keep in contact today. He is 86 years old now and we still write letters back and forth. I recently had the privilege of sending him my promotion letter. The sheer excitement of sharing that promotion with him was incredibly meaningful.”
“Without him believing in me I don’t think I would be sitting here talking to you about this promotion today,” she added. “He believed in me during a time when I didn’t believe in myself.”
Supporting Women in STEM
In an effort to promote mentorship and address female-specific concerns in the STEM fields, such as wage negotiation and salary differences, MU recently started its first Women in STEM group. The group was spearheaded by Rosenfeld and Azizan-Gardner, and had its first meeting in July.
“The issue of mentoring is something that you see everywhere, not just here,” said Azizan-Gardner. “It is a pervasive problem we need to address. And we can do that here at MU and do something that will really benefit everyone.”
Female mentorship is something that Rosenfeld believes is critical for female scientists and she makes an effort to mentor female undergraduate and graduate students.
“When you’re struggling, you often think that there is no way you can do this,” said Rosenfeld. “But if you see someone that looks like you that has succeeded and is teaching you, all the sudden your goal does not seem impossible.”
Mitchum is another strong proponent of mentorship and undergraduate research. She has mentored 26 undergraduate researchers in her lab, and 12 of them went on to graduate school, while many of the rest went to medical school.
“It’s so important for us as mentors, female or male, to believe in and encourage the younger generation,” she said. “I believe in many cases, you just need someone to believe in you and know you can accomplish things. It’s important to have quality in mentorship — investing in students and giving students your time and direct attention.”
Rosenfeld hopes that the Women in STEM group will empower female scientists to be more assertive. She said the first meeting was “eye opening” because many of the participants had similar experiences and it was powerful to hear their frustrations. About 20 women attended the first meeting, and Rosenfeld is confident that number will increase.
Azizan-Gardner believes that Bond LSC has the potential to be a leader in promoting, recruiting and retaining female scientists. And as a result, will encourage more women to go into STEM fields.
“I hope having a strong Women in STEM group will be great recruitment as well for other general faculty to come to MU,” said Azizan-Gardner. “At least that’s my goal, and that’s the area I’m responsible for. And on top of that, I think it will really entice other undergraduate women to go into STEM.”
Scientists prove parasite mimics key plant peptide to feed off roots By Roger Meissen | Bond LSC
When it comes to nematodes, unraveling the root of the issue is complicated.
These tiny parasites siphon off the nutrients from the roots of important crops like soybeans, and scientists keep uncovering more about how they accomplish this task.
Research from the lab of Bond LSC’s Melissa Mitchum recently pinpointed a new way nematodes take over root cells.
“In a normal plant, the plant sends different chemical signals to form different types of structures for a plant. One of those structures is the xylem for nutrient flow,” said Mitchum, an associate professor in the Division of Plant Sciences at MU. “Plant researchers discovered a peptide signal for vascular stem cells several years ago, but this is the first time anyone has proven that a nematode is also secreting chemical mimics to keep these stem cells from changing into the plant structures they normally would.”
Stem cells? Xylem? Chemical mimics?
Let’s unpack what’s going on.
First, all plants contain stem cells. These are cells with unbridled potential and are at the growth centers in a plant. Think the tips of shoots and roots. With the right urging, plant stem cells can turn into many different types of cells.
That influence often comes in the form of chemicals. These chemicals are typically made inside the plant and when stem cells are exposed to them at the right time, they turn certain genes either on or off that in turn start a transformation of these cells into more specialized organs.
Want a leaf? Expose a stem cell to a particular combination of chemicals. Need a root? Flood it with a different concoction of peptides. The xylem — the dead cells that pipe water and nutrients up and down the plant — requires a particular type of peptide that connects with just the right receptor to start the process.
But for a nematode, the plan is to hijack the plant’s plan and make plant cells feed it. This microscopic worm attaches itself to a root and uses a needle-like mouthpiece to inject spit into a single root cell. That spit contains chemical signals of its own engineered to look like plant signals. In this case, these chemicals — B-type CLE peptides — and their purpose are just being discovered by Mitchum’s lab.
“Now a nematode doesn’t want to turn its feeding site into xylem because these are dead cells it can’t use, so they may be tapping into part of the pathway required to maintain the stems cells while suppressing xylem differentiation to form a structure that serves as a nutrient sink,” Mitchum said. “To me that’s really cool.”
This means these cells are free to serve the nematode. Many of their cell walls dissolve to create a large nutrient storage container for the nematode and some create finger-like cell wall ingrowths that increase the take up of food being piped through the roots. For a nematode, that’s a lifetime of meals for it while it sits immobile, just eating.
But how did scientists figure out and test that this nematode’s chemical was the cause?
Using next generation sequencing technologies that were previously unavailable, Michael Gardner, a graduate research assistant, and Jianying Wang, a senior research associate in Mitchum’s lab, compared the pieces of the plant and nematode genome and found nearly identical peptides in both — B-type CLE peptides.
“Everything is faster, more sensitive and we can detect things that had gone undetected through these technological advances that didn’t exist 10 years ago,” Mitchum said.
To test their theory, Xiaoli Guo, postdoctoral researcher and first author of the study in Mitchum’s lab synthesized the B-type CLE nematode peptide and applied it to vascular stem cells of the model plant Arabidopsis. They found that the nematode peptides triggered a growth response in much the same way as the plants own peptides affected development.
They used mutant Arabidopsis plants engineered to not be affected as much by this peptide to confirm their findings.
“We knocked out genes in the plant to turn off this pathway, and that caused the nematode’s feeding cell to be compromised. That’s why you see reduced development of the nematode on the plants.”
This all matters because these tiny nematodes cost U.S. farmers billions every year in lost yields from soybeans, and similar nematodes affect sugar beets, potatoes, corn and other crops.
While this discovery is just a piece of a puzzle, these pieces hopefully will come together to build better crops.
“You have to know what is happening before you can intervene,” Mitchum said. “Now our biggest hurdle is to figure out how to not compromise plant growth while blocking only the nematode’s version of this peptide.”
New outreach program teaches CAFNR students to make plant science knowledge accessible to a younger audience Written by Stephen Schmidt | Science Writer in the College of Agriculture, Food and Natural Resources
Although abundant light was shining through the windows, it was the quiet before the storm. Andrew Ludwig, a University of Missouri sophomore majoring in plant sciences, surveyed the small tables and chairs spread out before him in the laboratory of the Benton STEM Elementary School on a recent Monday afternoon. He sifted through his notes. He was ready, even though it was his first time stepping foot in the building — and he was about to talk to a crowd of students spanning from the first to the fifth grade.
“I’m just going to try to stay enthused about everything because I’ve talked to some of my friends who are education majors and the big thing with conveying information to them is just being enthusiastic about it,” Ludwig said about his strategy on the “How Do Flowers Drink?” presentation he was about to give with fellow MU student Michael Gardner.
“I think the key is keeping them moving along, keeping them interested, because as soon as you lose their attention, they’re going to do whatever they want to do, so it’s going to be keeping things moving along at a pace that they’re still getting it, but that they’re not bored out of their minds,” added Gardner, who is a fifth-year graduate student specializing in plant stress biology. “We’re talking about water transport in a plant, which is a concept you can spend a semester on in a college-level course and still not be considered an expert on the topic.”
Both Ludwig and Gardner are a part of the team at the Bond Life Sciences Center lab of Melissa Mitchum, an associate professor in the Division of Plant Sciences. It was Mitchum who was able to launch the new “It’s All About Plants” series this spring with the Benton Elementary Science Club thanks to the science outreach portion of a new National Science Foundation grant that will further delve into a deeper understanding of the interactions between plants and parasitic nematodes she received in August and a partnership with the MU College of Education’s ReSTEM Institute, MU Office of Undergraduate Research and Columbia Public Schools.
The end result is a program that fosters learning of all varieties: The elementary students learn about plants, while the college students learn how to take complex ideas and break them down to a more accessible level. Furthermore, the program pairs undergraduate students such as Ludwig with graduate students such as Gardner and principal investigator mentors from across campus — involving the existing NSF-funded initiative Freshman Research in Plant Sciences (FRIPS) and the Students for the Advancement of Plant Pathology (SAPP) in the process.
“I think it’s a challenge for all of us who have advanced degrees to really think about where we were long ago and bring the concepts down to a basic level,” Mitchum said, “but I think it’s very important for us to be able to communicate our science at that level to really get the kids excited about research.”
She added that the program “really reinforces the concept of engagement and active learning.” In particular, it reinforces hands-on learning through a variety of activities. “I think that makes a big difference in learning,” said Mitchum, who will have sat with the children for five of the 10 presentations that started on Feb. 22. “I think that’s one of the reasons why I’m such a strong advocate of undergraduate research and getting in a lab and learning how to work in a lab. The same thing applies here. When the kids are doing experiments in the science club, they’re going to retain that information a lot more.”
School’s in session
“Class! Class! Class!”
“Yes! Yes! Yes!”
With those loud words reverberating through the room Ludwig had the attention of those before him — for a moment, anyway. The chatter had quieted down as he began to explain the main activity of the day, which would involve carnation flowers and six solutions of household items (sugar, salt, baking soda, vinegar, soda and food coloring) mixed with water in the same-sized cups – and one scenario with just water.
With the help of several volunteer MU students (whose hours are coordinated by Mitchum’s co-PI, Deanna Lankford, a research associate in the College of Education), the assignment was to pour 100 millimeters into each one of the cups.
The cups were then labeled with the name of the solution. This procedure was repeated three times. The white carnations were then cut to the height of the cup and placed in the water as a discussion ensued on what solutions would help the plant (besides plain water) and which ones would hurt.
Afterwards through the help of a video, the class was introduced to the idea of setting up controls and variables. The one variable, in this case, was the solution. All other factors (such as flower height, flower type, cup size and amount of liquid) were controlled, Ludwig explained. “We use the control to compare our other variables,” he said.
A moment later, Ludwig posed a question to the class: “Raise your hand if you think putting the flower in food coloring is going to change the color of the flower.” A collection of hands sprouted upward.
“We have some flowers that we put in the dye yesterday,” Ludwig continued, as he unveiled carnations that had white petals either tinged in red or blue to pass around to the class.
“I was right!”
“I knew it!”
“Do we get to keep them?”
A white carnation begins to show traces of blue food coloring in its petals after sitting in a solution with food coloring and water for a short period of time.
Following a brief video showing a similar experiment relating to celery and food coloring, Gardner explained the phenomenon to the class: “The plant is basically a big straw, so as the water evaporates up the plant, it pulls more water with it and then the food coloring too, so it gets to the very top of the plant, either the leaves of a tree or the top of a flower, and when it gets there the water will be able to evaporate, but the food dye can’t so that’s why your flowers are turning blue or red, OK?”
The food coloring portion of the afternoon turned out to be the top highlight for many of the participants. When asked about all of the projects he had worked on during the spring, Amahdrion Bradshaw, a second grader, proclaimed that “the funnest one was about dying the plants.”
Haily Korn, a fellow second grader, agreed, saying that her favorite part of the program is when you “do fun experiments” and that her favorite experiment was “when you get to dye stuff.”
A perfect fit
Lankford and the ReSTEM Institute formed the Benton Elementary Science Club, which meets one afternoon every week during the school year, seven years ago — the same time Benton officially became a part of the STEM (Science, Technology, Engineering and Mathematics) program.
“The science club has allowed our students to continue to expand their understanding of a variety of science topics through hands-on experiences after school,” said Heather McCullar, a STEM specialist who works at Benton. “The kids always leave club excited to share what they have learned with their families.”
Over the years, Lankford has helped many principal investigators with the education portion of their grants. When Mitchum asked her about getting involved with an existing partnership, Lankford immediately thought about the science club with its previously established learning format.
“Melissa said ‘I need help with this.’ And I said ‘Great, let’s talk,’” Lankford said, “And we did and we came up with the idea and it has been wonderful. I really like the fact that we have mentors and mentees doing the presentations.”
Under Mitchum’s direction, a series of meetings were set up with mentors and mentees last fall to develop the curriculum and lesson plans that would form the backbone of the course. Given that the grant is funded for a total of three years, the plan is to continue to teach the “It’s All About Plants” program, which has been well-received by students and school administrators alike, at Benton next spring.
Besides Mitchum, the other PI mentors from CAFNR who have taken part in the program are Gary Stacey, Curators Professor of Plant Sciences; Lee Miller, assistant professor of plant sciences; Xi Xiong, assistant professor of plant sciences; Walter Gassmann, professor of plant sciences; John Boyer, Distinguished Research Professor of Plant Sciences; Harley Naumann, assistant professor of plant sciences; Kevin Bradley, associate professor of plant sciences; Heidi Appel, senior research scientist, plant sciences; Jack Schultz, professor of plant sciences and director of the Bond Life Sciences Center; and Scott Peck, associate professor of biochemistry. PI mentors from the College of Arts and Science Division of Biological Sciences included Paula McSteen, Chris Pires, and Mannie Liscum.
The CAFNR students who took part in the science club series planning also recently hosted an outreach booth on t the Science Sleuth event on “Plants and Microbes” the MU campus April 16. In addition, Mitchum gave a talk at the Exploring Life Sciences symposium at the Bond Life Science’s Center recent Missouri Life Sciences Week.
Furthermore, the end goal is to take all of the lessons that are being created and turn them into a booklet that is easily accessible for teachers in Columbia Public Schools, and beyond, by posting the material online.
In the meantime, the lessons are being molded by the interactions of CAFNR students and those at Benton.
“You have some students who can’t write their names yet, and other people who know everything we’re trying to tell them before we start,” Gardner said, afterwards, referring to the beginning of the class when a student at the front of the room recited a brief and succinct view of a plant’s water transport system. “Apparently his grandma told him all of this stuff already. So yeah that was definitely a challenge that I think we did OK at it.”
“I think it’s really great for everyone involved from the elementary school students who are getting to learn about specific topics from people who are very well informed about it to undergraduate and graduate students who are getting a wider arrange of presentation skills,” Ludwig added. “You can get locked in your head about your research. It’s good to be reminded that the knowledge we gain through research also has a real-world application and that part of the scientific process is sharing.”
It’s a challenge that Mitchum said could serve as a benefit to anyone in the scientific community.
“It’s not easy for us to do many times,” Mitchum said of breaking complex idea down into something easy enough for a child to understand, or even an average adult. “It takes practice. So. It’s something we have to learn. Science communication is very important these days. Especially when we talk about what we’re doing in a lab, it’s very molecular, very cellular, but we have to find a way to make it relevant.”
She added that programs such as this one show children that not all scientists have “crazy hair with the goggles and lab coat. They see ‘Oh, these guys are just like everyday people.’ This is a realistic career for them.”
Would Amahdrion be interested in such a career path?
“Nope,” he said. “I want to be a basketball player.”
Still, when given the choice of attending the science club sessions or just going home after school, he has a quick reply: “Spending extra time at school because you learn more.”
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.
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.
“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.”
Beneath a North Carolina field in 1954, a tiny worm inched its way through the soil and butted against a soybean root. The worm pierced the plant, slipped inside and inserted a needle-like appendage into a cell. It pumped a mixture of proteins into the root cell and waited for the potent blend to take effect on the unsuspecting soybean.
Since the first detection of soybean cyst nematode (SCN) in the US, the worm Heterodera glycines has spread to about 80 percent of American soybean fields. In Missouri, SCN attacks soybeans in almost every county and causes decreased yields even in robust, healthy-looking fields. Nationwide, SCN wreaks havoc to the tune of $1.2 billion per year, making it by far the most costly soybean pest.
Despite the hefty toll, farmers still depend on the same small handful of resistant soybean varieties to combat SCN that they have used for years. But those natural defenses are becoming less effective as nematodes evolve.
“More than 90 percent of the soybean cultivars that farmers plant derive their resistance from a single source,” said Melissa Mitchum, a plant nematologist at the University of Missouri Bond Life Sciences Center and Division of Plant Sciences faculty member in the College of Agriculture, Food and Natural Resources. “Consequently, this has led to widespread virulence in the pathogen population, thereby reducing the effectiveness of those resistant cultivars.”
But in the past 10 years, researchers studying SCN have made numerous breakthroughs, unlocking the secrets of the nematode and exploring how the worm interacts with host plants. Now, scientists are poised to bring that knowledge from the laboratory to the field.
Found in translation
Relatively little was known about SCN a decade ago.
Scientists could determine the type of nematode in a soil sample and had just figured out the cocktail of proteins a nematode pumps into the soy root cell that transform it into a syncytium, or feeding cell.
Working in part with funding from commodity boards and farmer checkoff dollars, researchers around the country made breakthrough after breakthrough, deepening our understanding of SCN and equipping scientists with new tools to fight the pest.
That money helped scientists sequence the soybean genome, draft a SCN genome and pinpoint important soy and SCN genes.
Checkoff investments continued to pay dividends in 2012 when Mitchum and colleagues cloned the first gene linked to natural soybean cyst nematode resistance. This breakthrough is one key step in moving science from the laboratory into the field. With a SCN resistance gene in hand, new avenues for creating soybean varieties that fight off the nematode are opening up.
But other areas of research also hold promise in the struggle against soybean cyst nematode’s parasitic ways.
Mitchum’s group also identified the plant receptors that recognize and respond to the blend of proteins an attacking nematode inserts into a plant. In a recent project published in Plant Biotechnology Journal, Xiaoli Guo, a postdoctoral fellow in Mitchum’s lab demonstrated that silencing those receptors in soybean roots helped the plant resist SCN.
This work has implications for more crops than just soybeans: Working with collaborator Xiaohong Wang at Cornell, Mitchum’s group used their understanding of plant receptors to develop a potato resistant to potato cyst nematode.
A roadmap for discovery
To build on the momentum of recent research, experts drafted a roadmap for the next decade of nematode research. Their goal, Mitchum said, is to address the challenge of translating these research breakthroughs into something tangible for the farmer.
With support from state farmer run organizations such as the Missouri Soybean Merchandising Council, the North Central Soybean Research Program and the United Soybean Board, researchers are formulating teams that “bring together commodity, industry and university funding to develop collaborative, interdisciplinary, multistate projects,” said Mitchum.
And there’s plenty of scientific firepower to advance research: MU’s College of Agriculture, Food and Natural Resources alone has more than 90 faculty studying plant science, plant genetics and other areas of agriculture-related science.
The scientists’ plan for the next 10 years involves a blend of molecular research, plant breeding, population biology and outreach. Researchers will focus on refining the existing draft SCN genome, which will help to develop a quick, inexpensive test for HG type and eventually contribute to understanding of how SCN overcomes a plant’s resistance. They’ll create an “atlas” of SCN genes researchers can use to block the pest. Updating yield loss estimates and mapping SCN distribution will also give scientists a better idea of the nematode’s national impact. Other efforts will allow breeders to incorporate new sources of resistance into commercially-available varieties, refine the use of non-host species to control SCN and develop a pipeline for creating and testing transgenic SCN-resistant soybeans. Finally, videos, webinars and training modules will help scientists, students and producers take advantage of new discoveries and techniques.
Onward with research
A thorough understanding of SCN resistance and virulence starts with basic research and then moves into the field. “We all need to come together to transfer this knowledge to the breeder,” Mitchum said, “and from there it gets out to the farmer.”
Her lab recently received a National Science Foundation grant to continue their work on soybean protein receptors. Specific targeting of the receptors is just one potential strategy for producing new kinds of SCN-resistant plants. A second grant, from the National Institute of Food and Agriculture, will allow the lab to continue refining their understanding of how SCN proteins overcome a host plant’s defenses. To that end, Mitchum’s graduate student Michael Gardner is identifying the genetic blueprint of the different SCN types present in Missouri fields.
“If we better understand nematode populations and what makes those populations distinct, we can better advise farmers confronted with virulent nematodes,” Gardner said. “We’ll be able to go one step beyond the HG type test and understand how nematodes are able to adapt in the long term, not just the next growing season.”
But these breakthroughs do little good unless they then become useful tools for breeders and ultimately farmers. To that end, Mitchum and other researchers will help breeders use research results to produce soybeans with durable resistance. They‘ll also develop guides so farmers can easily incorporate new technologies and management strategies into their farms.
It’s important for farmers, breeders and researchers to take a unified approach to fighting SCN, Mitchum said, because a tactic that seems successful at first could backfire.
For instance, combining resistance genes in a single soybean variety could actually be harmful. “When we deploy it in the field, we select for nematodes that can overcome multiple types of resistance,” Mitchum said.
A better approach might be to perfect varieties with distinctive resistance mechanisms and insure durable resistance by rotating among the resistant varieties and non-host crops.
“It’s similar to taking antibiotics,” Mitchum said. “Improper use and overuse selects for resistance.” The strategic planning document should help everyone working with soybeans and SCN leverage and build upon new knowledge.
Despite all the research and recent breakthroughs, there remains only one certainty in the ongoing arms race between soybeans and SCN: “It is highly unlikely that we will eradicate it.” Mitchum said, “We’re going to have to find new strategies to protect and bolster soybean yields.”
Thanks to the efforts of researchers such as Mitchum, in the future SCN might be a little easier to get along with.
University of Missouri Plant Nematology Laboratory: An extensive legacy
Bob Heinz spent his last day at work in December surrounded by nematodes. Heinz served as Mitchum’s research specialist and coordinator of the Plant Nematology Laboratory, where he processed soil samples, responded to growers and assisted researchers. After 35 years on the job, he’s retired, and Amanda Howland is now filling his shoes. The scientists and farmers who’ve worked with Bob over the decades thank him for his dedication and wish him luck in his retirement. And Amanda: Welcome aboard.
The Plant Nematology Lab, housed within Mitchum’s lab at MU, represents a successful model for how research, teaching and extension program integration can promote interdisciplinary collaboration. Such an approach helps maintain an effective pipeline that brings research-based information and resources from MU to Missourians. The lab offers an array of tests that help farmers understand and manage nematode populations. The available tests include:
–Vermiform Nematode Identification: Soybean Cyst? Root Knot? Lesion? Find out what kinds of nematodes are in your fields with this test.
–Soybean Cyst Nematode Egg Count: This procedure provides an estimate of the number of SCN eggs in your field.
–Soybean Cyst Nematode HG Type Test: Different types of SCN have overcome various sources of soybean resistance. A HG type test will help you determine the best source of resistance for the particular type of SCN in your field.