Gender BenderPosted in: Technology By John Dietz December 1 2013
Burkhard Schulz is a skilled gene hunter, and he’s bagged a winning prize for agriculture research.
Schulz, a professor in Purdue University’s Horticulture and Landscape Architecture faculty and an associate editor of Frontiers in Plant Physiology, made a seemingly simple discovery three years ago that could have a staggering effect on agricultural research and crop production in the years ahead.
Schulz came up with a methodology for regulating plant steroids. It has many implications — including enabling plant breeders to develop shorter corn varieties with lower fertilizer inputs and higher yields, translating into huge potential savings for producers.
And the boon doesn’t end with corn. The process of regulating plant steroids could be applied to any flowering plant, says the German-born Schulz, including corn, sorghum, wheat, barley, rice, vegetables and fruit trees.
By knocking out certain steroids, biotech researchers have opened a whole new gateway into plant genetics. In this new reality, even the sexual orientation of corn is up for grabs.
Schulz made his discovery while investigating the genetic mechanisms that control plant ‘architecture’ as seeds open, grow into shoots and develop a variety of organs such as roots, flowers and fruits.
Scientists knew that natural plant steroids play a crucial role in plant growth. They just needed a tool to unlock the doorway to studying how these hormones work inside the plant.
Discovering such a tool would be like unlocking the entrance to a factory — finally scientists would be able to see what was regulating growth. In corn, for example, what determines the number of nodes, the length of the stalk, the cobs and kernels and flowers?
Schulz’s curiosity for understanding how plants grow emerged at a young age. At eight, he watched a television documentary about James Watson and Francis Crick; two scientists who helped discover the structure of DNA.
“I scribbled down the structures but I had no clue what it was about,” Schulz recalls. “I was totally fascinated by it.”
About 10 years later, as a freshman at the Free University of Berlin in 1980, Schulz heard a talk by visiting Belgian plant molecular biologist Jeff Schell, a pioneer in genetic engineering who focused on the interaction between plants and soil bacteria.
“He figured out how bacteria are naturally able to transfer DNA into plants,” Schulz recalls. “It opened up the door to all the modern plant biotechnology.” Schulz was hooked. “I thought, ‘Wow, this is something that will really change the world.’ And it did.”
At that time, there was not a single transgenic plant in a field. Still, Schulz left the talk with a vision about how this transfer of DNA could change the future of agriculture.
“[Schell] made the right predictions about what would happen in the future, and that gave me the impetus to go in a particular direction with my studies,” says Schulz. “So I became a gene hunter.”
Corn on Steroids
Gene hunters use molecular biology, biochemistry and genetics to investigate why and how cells differentiate into the plant structures we know as stems and leaves, fruit and seed.
“We look at how whatever affects yield has to do with the architecture of the plant,” he explains. “Bigger fruit, more seed, more biomass, more branches — all these things are architectural definitions.”
This deeper understanding becomes the foundation where plant breeders can find and build pathways to characteristics that are important to farmers.
In doing this work, Schulz and his colleagues ask very basic questions, such as: What actually regulates the expansion of cells? Why do most corn plants have six stem segments below the ear and a couple above the ear? And is it possible to change that ratio?
At Purdue University in 2005, Schulz established a research program to investigate the regulation of plant architecture, called the “Three-dimensional Organization of Plant Structure.”
“If plants do not produce these steroids, they end up very small,” says Schulz. “If you know what regulates the expansion of cells, then you know what regulates the size of organs such as leaves and stalks, or the number of internodes.”
More than 70 steroid hormone molecules, known as brassinosteroids, have been isolated from plants since 1979. They are involved in cell expansion and elongation, pollen formation, protection from cold and drought, tissue growth and senescence, and the aging process after a plant is mature.
To open and explore the complex genetic factory, Schulz needed the proverbial needle in a haystack — an affordable chemical that would inhibit production of these steroids in a predictable way and enable him to produce ‘model’ greenhouse plants. With these in hand, he could hunt for matching plants in a natural population and isolate the genetic differences for plant breeders.
He started with corn in 2007 and a synthetic steroid inhibitor that cost $25,000 per gram. Brassinazole did shut down steroid production as he expected and proved the concept, but was far too expensive to use for this type of research in crop plants. As well, it was in short supply and he would need many kilograms over a period of years to do the work he contemplated.
So Schulz turned to fungicides that have a similar chemical structure to brassinazole for a possible growth regulator. He found several over the following years that could serve the purpose.
“We were lucky,” he says. “We found fungicides that allow us to inhibit biosynthesis of steroids in any plant, not just corn. We have tested this now with 10 different species and it always works.”
For now, Schulz is working with propiconazole, an older broad-spectrum fungicide. Propiconazole is widely used in agriculture and is also popular on golf courses, where it prevents ‘dollar spot’ disease. It is recognized as safe for humans and food crops; it also is more potent than brassinazole for inhibiting steroids.
The fungicide costs 10 cents per gram and about $25 for a single trial, he says. As a research tool in the lab, and as a methodology for plant research, Schulz says this new method opens the door to research avenues that have never been possible.
In the future, Schulz thinks, this particular fungicide also may be able to regulate the growth rate of turf grass.
Breeders’ Dream: Feminized Corn
Using propiconazole in the greenhouse corn, Schulz eliminated brassinosteroid production. The result? Dwarfed and neutered corn plants. The plants, with genetics to grow eight feet tall, reach only 30 inches after treatment, and they fail to produce male organs. Where male pollen-producing tassels should be present, they have female corn ears.
The male aspect of flowering corn became ‘feminized’ when the steroids were removed. “Hermaphrodite is a good term for it, because the male organs develop into female organs,” Schulz says.
Corn has an unusual reproduction strategy. In the plant kingdom, most flowering plants contain the masculine and feminine reproductive organs side by side in the same flower. With corn (and cucumbers and melons), the male and female organs are separated. Male tassels at the top of the stem produce pollen; it fertilizes emerging silk on side branches along the stem, to become female ears bearing the seeds.
“If you block the production of steroids, the top male flower turns into a female flower that looks more or less like a branched ear. [Tassels are always branched in corn; ears are not]. This means it is feminized,” Schulz says.
The neutered or ‘hermaphrodite’ corn still has male genes but fails to produce the steroid hormones that are required for producing pollen, the fundamental male characteristic.
Road to Commercialization
Down the road, this could pave the way for seed companies to feminize corn easily (and cheaply) for low-cost hybrid seed production. For the past century, hybrid corn has been produced manually by cutting off all the tassels of the male flowers — a favorite summer job for generations of high school students in the corn-belt.
The feminized corn plants also are shorter. However, this steroid-free dwarf corn continues to have normal cob production and an ‘extra’ set of ear-like tassels.
The potential for farming is huge. “Short plants, with no loss of yield, are much sturdier against wind and rain and weather,” says Schulz. “Short plants also need much less water and nutrients to produce the same amount of seed.”
Once he achieved a number of steroid-free plants in the greenhouse, the gene hunter recorded the detailed characteristics and then searched the research fields at Purdue for untreated plants with the same set of ‘symptoms’ or phenotype.
It amounts to a shortened way to find the needle in the haystack. The true mutant can then be studied for its genetics and biochemistry. To date, Schulz and his coworkers have found mutations in three important steps of the steroid biosynthesis in corn. In all cases, the plants were small and feminized.
Together with another Purdue research team, he is now is working on a field application for propiconazole to moderate steroid production. The plants will produce normal flowers but may be 30 to 40 percent smaller.
“We are studying how much we have to apply, and how often, to really turn the male into female.” he says. “If we can identify an exact timing to treat plants to prevent males from developing, then we have a product to market.”
“If we reduce the biomass by 10, 20 or 30 percent, we could still get the same amount of seeds. And propiconazole is a powerful anti-fungal agent that really attacks every fungus. You make your plants very resistant to fungal infections.”
Meanwhile, now that the fungicide has opened the gateway, Schulz and his group are working to untangle the mysteries related to brassinosteroid production.
They are applying the same process to other plants, with conventional flowering, and in other regions. They are producing taller sorghum with more biomass, and they are ready to look for the trait in barley, Schulz says.
“I have a student working on vegetables used in Kenya. They cannot grow them year-long, so we are starting experiments in treating these plants using the information we have on steroid biology because the steroids also have an effect on drought resistance,” he says.
“We want to learn as much as we can. This compound is regulating many, many different aspects of plant biology.”
Pathways for commercialization of this technology will happen through development of improved strategies for seed germplasm. Schulz says he’s working with seed companies, such as Ag Alumni Seed, a non-profit corporation founded by faculty from Purdue University to provide top quality seeds to producers throughout the world, as well as chemical companies such as Stoller Enterprises to work on ways to translate this research into an application farmers can use.
It’s hard to say when that will happen. “The timeframe to bring this technology to market depends on the commitment and investment by possible users and is not easy to predict,” he says. “As we work mostly with already approved and licensed compounds, the time to market should not be as long as in the case of novel compounds that need to go through extensive regulatory processes.”
The environmental concerns, he adds, are relatively minimal as the compounds have been in use as fungicides since many years. Propiconazole was first registered in 1981 for use on turfgrass and grass grown for seed. The EPA expanded the use to include several food crops in 1987, 1993 and 1994.
The research is also being applied in Canada — in barley. Ravi Chibbar, professor and Canada Research Chair in Crop Quality at the Department of Plant Sciences at the University of Saskatchewan in Saskatoon, is studying how steroids in barley influence the starch granule size.
“The more uniform the granules are, the better it is for brewers,” Chibbar says. His research team discovered a variant of barley with very uniform granules, which is ideal for malting barley. By conventional plant breeding, a mutated brassinosteroid receptor gene (uzu1) has been transferred to a Canadian barley variety that now produces homogenous starch granules.
“A lot of people have tried to produce uniform starch granules in barley, but this is the first time it has been achieved in the field,” says Chibbar.
Schulz’s work is aiding researchers in other regions, too. “In the immediate future, the work at Purdue is going to enable a lot of research that otherwise couldn’t have been done,” says Phil Becraft, professor of Genetics, Development and Cell Biology at Iowa State University.
Becraft is involved in identifying receptor genes in corn that perceive and respond to the brassinosteroid hormones. The brassinosteroid receptors compute the information of the steroids in the plant cell and activate genes that react to brassinosteroids. The receptor proteins ‘tell’ the plant cell that steroids are present.
In the past, he relied on traditional genetic research, which made the work almost impossible to finance. Schulz removed that barrier when he discovered a cheap fungicide that could regulate the hormone production.
“Now, to be able to just spray on a compound and study the response at the molecular level, the physiological level, the growth and architecture of the plant, disease resistance, stress resistance — that enables a lot,” Becraft says.
He adds, “We’ve altered some genes that we think are involved in growth and development. Burkhard’s work has provided an independent mechanism for testing the results. Controlling male flower production is only one of many possible aspects of this discovery.”
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