Scientists explore genetic similarities between plants and mice
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.
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.
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.”
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.
Plant scientist Ruthie Angelovici joins the Bond Life Sciences Center
By Jennifer Lu | MU Bond Life Sciences Center
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.”
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.
“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
“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.
“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
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.
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
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
“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.
Mutant arabidopsis models under lamps in Shuqun Zhang's lab.
Three-month-old mutant arabidopsis models are used to study the function of pollen.
The thought of pollen dispersed throughout the air might trigger horrific memories of allergies, but the drifting dander is absolutely essential to all life.
Science has long linked this element of reproduction with environmental conditions, but the reasons why and how pollen functions were less understood. Now lingering questions about the nuanced control of plants are being answered.
“Pollen is a very important part of the reproductive process and if we understand how pollen develops and how environmental stresses impinge on this process, we might be able to prevent crop loss due to high temperature or drought stress etc.,” said Shuqun Zhang, a Bond Life Sciences Center investigator.
Zhang has developed a new line of seeds that helped him and his lab identify an influential signaling pathway that triggers a chain reaction associated with normal pollen formation and function.
This research could lead to improvement to a plant’s response to disastrous environmental variables like drought to optimize pollen production and increase the production of food crops.
Left: Pollen grains genotypes MAPK3 and MAPK6 are illuminated by red and yellow dye using a fluorescent microscope. RIGHT: Normally developed pollen grains shown by an electronic microscope scan. | Credit: Shuqun Zhang
Seeds of success
Mutant seeds are the key to this work.
Instead of glowing green in the soil like you might see in a science fiction movie, they are providing important insight on plant reproduction and stress tolerance.
Zhang developed these plants from a mutant strain of Arabidopsis, a model plant used in scientific research. Certain genes were “switched off”to pinpoint where important pollen functions were signaled.
Using this mutant plant and seed system, Zhang found that WRKY34and WRKY2, two proteins that turn on/off genes, are regulated by MPK3and MPK6 “signaling” enzymes. These enzymes basically transform proteins from a non-functional state to a functional state, turning on specific duties or functions. Zhang, a professor of biochemistry at MU, began tinkering with the MPK3 and MKP6 pathways more than twenty years ago during his post-doc at Rutgers University.
Zhang’s research shows the newly identified MPK3/MPK6-WRKY34/WRKY2 pathway is a key switch in the hierarchy of the signaling system in pollen formation.
The research showed that the plant’s defense/stress response and reproductive process are linked, and the influential proteins MPK3 and MPK6 were part of the bigger WRKY34/WRKY2control pathway, which is activated in early pollen production.
The system is so useful that researchers across the country won’t stop asking for the seeds, Zhang said.
“We have a lot of requests for seeds,” Zhang said. “This is a very nice system to study pollen formation and function.”
The cascade of control
The functions of MPK3/MPK6 in plants can be compared to a “mother board” switch. The pathway — MPK3 and MPK6 —are part of a hierarchy of response, turning functions on or off. In other words, it’s a switch that controls a lot of different things. Controlling WRKY34/WRKY2 is one of the many roles played by MPK3 and MPK6.
Shuqun Zhang, University of Missouri Bond Life Sciences investigator.
“Whatever is plugged into it is what comes on,” Zhang said. “We are actually very, very interested in the evolutionarily context, how this came to be.”
This signaling process is just one of many in plants. MPK3 and MPK6 are two out the 20 MPKs, or MAPKs (abbreviated from Mitogen-Activated Protein Kinases) in Arabidopsis. They control plant defense, stress tolerance, growth, and development including pollen formation and functions.
“We determined that this MAPK-WRKY signaling module functions at the early stage of pollen development,” Zhang said.
The “loss of function of this pathway reduces pollen viability, and the surviving pollen has poor germination and reduced pollen tube growth, all of which reduce the transmission rate of the mutant pollen,” according to the research.
Zhang and his lab worked with the MU Division of Biochemistry and Interdisciplinary Plant Group on the research, which published in PLoS Genetics in June of this year.
A world without pollen production and defense
Without pollen, plants would not reproduce — there aren’t any Single Bars in the plant world (that we know of) — and if plant generations don’t propagate, there would be no air or food for human life to sustain.
“The factors such as heat and drought stresses cause problems to the plant’s normal developmental process and that’s how pollen fails to develop,” Zhang said. “If we understand the process, and know how environmental factors impact negatively the process, we can then make plants that can handle environmental stress better.”
Zhang and his lab continue to research the complexities of these pathways. Next on the quest is to answer how MPK3/MPK6 are involved in pollen functions such as guiding the pollen tube growth towards ovule to complete the sexual reproduction process in plants.
“It is possible that MPK3 and MPK6 are activated quickly in response to the guidance signals,” he said. “There’s still a long way to go because very few players in this process have been identified, we try to understand the biological process how they work together.” This research is in collaboration with Dr. Bruce McClure, also professor of Division of Biochemistry.
Read more:
1. PLoS Genetics (May 2014): Phosphorylation of a WRKY Transcription Factor by MAPKs is Required for Pollen Development and Function in Arabidopsis — Funded by a Hughes Research Fellowship and grants from the National Science Foundation.
2. Plant Physiology (June 2014): Two Mitogen-Activated Protein Kinases, MPK3 and MPK6, are required for Funicular Guidance of Pollen Tubes in Arabidopsis — Funded by a National Science Foundation grant and a NSF Young Investigator Award.
