FEATURES • Summer 2002

Collaborating with students and peers, Professor Barbara Schaal researches the evolutionary genetics of plants in hopes of enriching crops such as cassava and rice.

by Janni Simner

Rice flour muffins and cassava cheeseballs are not ordinary student fare—unless you're in Barbara Schaal's undergraduate Plants and Civilization class.

"Because we're learning about the human uses of plants, every day she brings in something we can taste, usually some exotic plant that we've never seen before," says Brian Hamman, A.B. '02.

For plant geneticist Schaal, it's just one more way of passing on the enthusiasm she feels for her subject. That enthusiasm has informed her teaching at all levels, and her own quest to better understand evolutionary history—a quest whose results ultimately may improve the very crops she encourages her students to sample.

She first learned about one of these crops through the enthusiasm of another researcher, Robert Bertram of the U.S. Agency for International Development. Bertram came to her lab in 1989 bearing wild plants from South America and Mexico. The plants were all members of the genus Manihot, and Bertram wanted to trace the evolutionary origins of their domesticated relative, Manihot esculenta, commonly known as cassava.

"I didn't know what cassava was," recalls Schaal, who was recently named the Spencer T. Olin Professor of Biology in Arts & Sciences, and who also holds an appointment as professor of genetics at the School of Medicine. "But I said I was sure we could find its ancestors." Doing so proved more complicated than Schaal first anticipated, but it ultimately proved of great importance.

Most Americans have sampled cassava as the main ingredient of tapioca pudding. For residents of sub-Saharan Africa, however, the starchy underground stems of this plant serve as the population's number one source of calories. The Portuguese had brought cassava to Africa more than 300 years ago. Some scientists thought the plant descended from a wild ancestor in Mexico; others suspected it was a hybrid of several "parent" plants—but no one knew for certain.
Professor Barbara Schaal (center, left) and Associate Professor Gayle Fritz (center, right) took students from their joint anthropology-biology course—Plants and the American People: Past and Present—to Tucson, Arizona, over spring break. Visiting Native Seed Search, the class learned about crop varieties used by Native Americans in this desert region. The course is part of an Arts & Sciences initiative fostering interdisciplinary teaching and research.

 

That ignited Schaal's enthusiasm, and also her sense of justice. "Here was the sixth most important food crop in the world, and we didn't even know where it had been domesticated. That just didn't seem right." Especially since, as a non-native plant, cassava lacked resistance to African diseases such as the cassava mosaic virus, which regularly reduced food yields and caused famines. If found, cassava's progenitor or progenitors could potentially increase the genetic diversity—and thus the disease resistance—of cassava crops.

Schaal, who had already answered evolutionary questions about native North American plants such as Mead's milkweed, began her research by looking for differences and similarities in the DNA sequences of Manihot species. Her work was collaborative from the start. She worked with Bertram; Washington University graduate student Kenneth Olsen, A.B. '91, Ph.D. '00; and Luiz Carvalho of EMBRAPA, the Brazilian Agriculture Research Corporation.

Ordinary DNA sequencing soon proved inadequate. Manihot's history included a period when the number of species increased relatively rapidly, and this made analysis difficult. Schaal shifted her focus, examining rapidly evolving portions of individual genes.

The technique she used relied on a polymerase chain reaction (PCR), which is the genetic equivalent of a high-speed Xerox machine. A PCR takes double-stranded segments of DNA, "unzips" them, and uses each single strand as a template to create a new double strand. When the process is allowed to repeat itself continuously, millions of copies can be created in a few hours. The result was that Schaal's initially small gene samples could be amplified into something "large" enough to study.

Using the resulting data, Schaal and Olsen began recreating cassava's family tree. Their focus turned to a single gene, glyceraldehyde 3-phosphate dehydrogenase. Cassava's origins gradually became clear. The plant descended from a single subspecies, but not one found in Mexico. Rather, cassava's ancestor was the Manihot esculenta subspecies flabellifolia, which grows on the southern border of the Amazon River Basin in Brazil.

In 1999 Schaal and Olsen published this finding in the Proceedings of the National Academy of Sciences of the United States of America, as well as in the American Journal of Botany and Molecular Biology and Evolution. Varieties of flabellifolia have already been placed in germplasm collections, and some native populations are now protected in conservation preserves.

Schaal finds this practical application immensely exciting. "It's wonderful to take basic scientific techniques and use them for applied problems," she says. "We not only get to better understand basic evolution, but the research has value beyond that, too." Addressing such applied problems has become as much a focus of Schaal's work as the theoretical questions she strives to answer.

"It's wonderful to take basic scientific techniques and use them for applied problems," Schaal says. "We not only get to better understand basic evolution, but the research has value beyond that, too."

"The impact of Barbara's work is felt worldwide," says Ralph Quatrano, chair of the Department of Biology and also the Spencer T. Olin Professor. "Not only has she been able to do this work, but its quality is so high." That quality is also recognized by many foundations that help fund Schaal's research, including the National Science Foundation, the Rockefeller Foundation, and the Guggenheim Foundation.

In her laboratory, Quatrano says, Schaal has a talent not only for asking the right questions, but also for encouraging the graduate students and others working in the lab to do the same. "When a graduate student comes in, I sit down and ask, 'What are you interested in?'" Schaal says. "We come up with a project that the student feels really passionate about."

Graduate student John Gaskin, whose research focuses on invasive plants, says this approach works well. "We take our ideas and run them by Barbara, and if they're good enough, we're free to pursue them." The result is a lab with a wide range of projects at any time: everything from analyses of plant stem anatomy and flower development to studies of disease resistance in tomatoes and the evolutionary origins of jacote, a tropical fruit.

A collaborative spirit permeates all this work. "We learn from the other students," Gaskin says. "The older students help the younger ones, and sometimes the younger ones know more than the older ones." He adds that Schaal herself "is very accessible. Her door is always open."

Schaal's accessibility extends to the larger Washington University community. As a member of the Curriculum Implementation Committee, she has worked with colleagues in other departments to improve students' undergraduate experience at the University. As a member of the Academic Planning Committee, she works with Edward S. Macias, executive vice chancellor and dean of Arts & Sciences, to help plan the overall future of Arts & Sciences. "A key member of our faculty, Barbara is a splendid teacher, a leader in her field, and an enthusiastic participant in our interdisciplinary endeavors," Macias says. "She brings excellent ideas and thoughtful, sensible advice to the wide range of issues that come before our Academic Planning Committee. I know that other faculty members, too, rely on her good judgment and want to work with her."

As a member of the National Academy of Sciences, Schaal takes her skills beyond the University into the larger scientific community. She serves on the Life Sciences Board of the academy's National Research Council, and she heads the academy's standing Committee on Agricultural Biotechnology, Health, and the Environment. In these roles she's helped advise the U.S. government on everything from stem cell research and science education to the effects of genetically modified plants on biodiversity.

Her own research remains concerned with theoretical genetic questions that have practical applications for the world's food crops. "I think the whole issue of hungry populations—and the social unrest that results—is a real concern for us all," she says. Her focus has shifted from cassava to rice, and she's begun looking at the migration of genes in Thailand's rice strains. She hopes to analyze the biodiversity of wild and domesticated varieties to understand what effect genetic modification of rice crops might have on rice species as a whole. Once again the project is a collaboration, this time with scientists at Chiang Mai University in Thailand. The work is funded by the U.S. Agency for International Development and the McKnight Foundation.

Schaal remains enthusiastic about both the theoretical and applied aspects of her work. "It gives me a lot of pleasure just to figure things out," she explains. "I basically want to comprehend better how the world works."

It is a goal in which all her collaborators play a part. "I really feel like we're cogs in a wheel," Schaal says. "We're all providing bits and pieces of information, and our goal is to slowly understand the natural world."

Janni Simner, A.B. '89, is a free-lance writer based in Tucson, Arizona.

 

 

 

 

Professor Barbara Schaal (left) is supervising Ana Caicedo's dissertation project, a study looking at the population genetics of disease-resistant genes in wild tomatoes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Researching Rice: Shifting her focus from cassava to rice, Professor Schaal has begun looking at the migration of genes in Thailand's rice strains. Collaborating with scientists at Chiang Mai University in Thailand, she is hoping to analyze the biodiversity of wild and domesticated varieties to understand what effect genetic modification of rice crops might have on wild rice species. (Photos of rice farmers, who are transplanting, threshing, winnowing, and drying their crops, are courtesy of Kanok Rekasem, Chiang Mai University.)