Biostatistics: Science by the Numbers
Google Search for "Work-Life Balance"
At the Intersection of Need, Science and Market
How Oats, Peas, Beans and Barley Grow
Brain Studies Yield Clues to Desire and Motivation
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How Oats, Peas, Beans and Barley Grow
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Valerie Oke '88 |
Whereas most people strolling through a field of sweet clover in summer hear only the hum of honeybees and rustling of tender leaves in the breeze, Valerie Oke '88 also is aware of an intimate conversation between the legume and the nitrogen-fixing bacterium, Sinorhizobium meliloti.
Oke, a biology professor at the University of Pittsburgh, studies the transformation of S. meliloti cells from vegetative bacteria into bacteroids in nodules on the roots of legumes, such as alfalfa and several species of sweet clover. Bacteroids are a distinct cell type that fixes atmospheric nitrogen into ammonia, which provides a usable form of nitrogen for plants. In this symbiotic relationship, the plant is able to survive in nitrogen-poor soil, and the plant provides nutrients to the bacteria.
Because this is a species-specific relationship, the partners must first introduce themselves. The plant exudes compounds from its roots, which identifies its species to the bacteria in the soil. When Rhizobium bacteria recognize those compounds, they produce "Nod factor," which identifies them to the plant. If the plant recognizes the bacteria as the right species, it forms nodules on its roots.
"We already knew about this conversation," Oke says, "but there are probably a lot of other molecular signals going back and forth because it is an incredibly intimate interaction."
Once the bacteria have infected the root nodules, they differentiate into bacteroids in "a process that involves an alteration of cell fate, presumably with an underlying developmental pathway," Oke says.
Gene Expression
Oke's lab uses a molecular genetic approach to identify and characterize the bacterial genes involved in the bacteria's infection of the nodule and its subsequent differentiation into bacteroids. "We are characterizing the roles of these genes during symbiosis by studying the functions of the gene products, testing for host-specific defects, and using genetic screens to identify the regulatory circuits that control gene expression during bacteroid formation," she says.
Oke says she knew she wanted to be a biologist from the age of 16, as an international baccalaureate student at Armand Hammer World College in Montezuma, N.M., where she wrote an extended essay about oncogenes. "I read my first few 'real' journal articles," she recalls, "and I got all fired up about biology."
At Bryn Mawr, Oke concentrated on molecular and cell biology, working with a Haverford College biologist, Kaye Edwards, on development in the worm, Caenorhabditis elegans. As a graduate student in cellular and developmental biology at Harvard University, she worked in a microbiology lab, where, Oke says, "I fell in love with microbiology." In 1997 she completed a National Science Foundation postdoctoral fellowship in plant biology at Stanford University. She joined Pitt's Department of Biological Studies in 2000.
Stress Response
The Rhizobium -legume relationship is usually described as a mutually beneficial symbiosis. "From the plant point of view, that is really obvious," Oke says, "because it interacts with this bacterium that directly provides it with nitrogen. From the bacterial point of view, it is less clear whether or not it is definitely beneficial. After entering the root nodule, the bacteria are trapped there until the plant degrades the soil, and many of them die."
Oke's research points to bacterial stress responses as a key to their survival in the root nodule. "We are studying how the bacterial cells live within a plant and identifying the challenges for them," she says. "I am fascinated by genes and regulatory circuits — which groups of genes are turning on to enable the bacteria to survive there?" Her research into S. melioti's RpoH protein-mediated stress response has implications for understanding the stress responses of bacteria in general.
However, Oke observes, "Money is tight in basic lines of research. Over the long term, that is a problem for our country because pure research can lead to a breakthrough that nobody could have predicted."
Today, Oke says, it is particularly difficult for a junior faculty member to generate the steady stream of grants that is essential to maintaining a basic research lab. "Even senior people who have never had trouble with funding are losing grants," she says. "People submit really good proposals, and they don't get funded. They have to submit them again, and again. And what gets rewarded is persistence. Meanwhile, how do you maintain your lab? I don't think anyone has come to terms with it."
Broadly, Oke's research is of interest to scientists who are studying ways to tweak the symbiotic relationship between crop legumes and various species of Rhizobium bacteria to produce more nitrogen and reduce agricultural dependence on nitrogen fertilizers, which are not only expensive, but also contribute to water pollution.
Oke recalls a traditional children's nursery rhyme that refers to three-field crop rotation:
Do you, do I, does anyone know,
How oats, peas, beans and barley grow?
"Only peas and beans can obtain usable nitrogen from symbionts," she says, "while the others must obtain usable nitrogen from the soil."
And she reflects on the potential benefits of basic research into the developmental relationship between bacteria and plants for crop production. "A real pie-in-the-sky goal is to extend this sort of symbiotic interaction to non-legumes," Oke says. "Imagine a world where rice did not need nitrogen fertilizer. That would be incredibly beneficial in terms of trying to feed the world while also protecting the environment."
Dorothy Wright contributes news and feature articles on science, technology, engineering and general-interest topics to a variety of publications, including Civil Engineering and Engineering News Record.