Unexpected discoveries could yield better crops, savings for farmers

Tuan-hua David Ho, Ph.D., investigates plants' amazing ability to resist environmental assaults

Tuan-hua David Ho, Ph.D. harvests seeds from a barley mutant in his laboratory. Ho studies ways to make plants more resistant to heat, drought, cold and soil salinity.

Sometimes when you are finding your way, it's better to go against the grain. Such is the case of Tuan-hua David Ho, Ph.D., professor of biology in Arts & Sciences. Ho was a 20-year-old junior biology student at National Taiwan University enthralled with plants when he attended guest lectures given by the esteemed Joseph Varner, Ph.D., then a professor of plant biology at far-away Michigan State University.

Rather than relax and soak in the knowledge like most students, Ho was one of just three students bold enough to take the lecture course for credit, which meant he had to pass a difficult oral exam afterwards.

"That oral exam was not easy, but I took it and did well," said Ho, relaxing in a conference room in Rebstock Hall. "I was very impressed with Joe, and evidently he was with me. He encouraged me to apply for graduate studies at Michigan State, and I got accepted ... . It was the only place I applied, and I went there hoping to learn from Joe."

Varner, who died in 1995, was a world-renowned plant biochemist. He later left Michigan State University in 1973 to begin his long, distinguished career at Washington University, where he recruited such outstanding plant biologists as Mary Dell Chilton, Barbara Schaal and Roger Beachy, to name just a few.

Ho's first exposure to Washington University was in 1974-76, when he came here as a visiting student finishing up his doctoral work with Varner, his adviser. His doctorate came from Michigan State, but "physically I was here for two very good years," he explained, "and I enjoyed the time very much."

Fast-forward to 1984. Ho, his wife, Berlin, and young daughter, Junlin, lived tranquilly amidst the vast expanse of corn and soybeans known as eastern Illinois, where Ho was a rising University of Illinois assistant professor of botany, studying how those cash staples and other grains protect themselves from cold, heat, drought, excessive salt and other environmental stresses.

He got a call from the Washington University biology department and an invitation to present a graduate seminar. He was happy to renew acquaintances and disseminate his knowledge; he drove the three-plus hours, gave the seminar to an impressed audience, drove back into the inky Illinois night, and the next day received an early-morning telephone call from the department, urging him to apply for an opening here. An offer soon followed.

Difficult choice

His colleagues would say that Ho would have been successful had he stayed at Illinois or gone elsewhere, but no one can disagree that his accomplishments here have been nothing less than outstanding. Collaborating at times with researchers throughout the world, Ho has made several landmark discoveries in plant biology that are leading to new understanding of plants' capabilities to protect themselves in harsh environments and of the action of two phytohormones, gibberellins and abscisic acid, which jointly regulate the seed germination process.

In the early 1990s, Ho made a surprising and confounding find in biotechnology. He and his group found a single gene, originally isolated from a barley plant under stress, that, when over-expressed in transgenic tobacco, rice and wheat, significantly enhances tolerance to drought and salinity stresses. The gene is one of a variety he helped discover in the late 1980s called late embryogenesis abundant (LEA) genes. They are important because they are expressed near the end of seed development, a time when the plant tissue is highly resistant to environmental stresses.

His discovery disputed long-held notions that such divergent traits could only be controlled by dozens of different genes and that these multigenic traits could never be genetically "programmed" into a plant.

Ho studies the molecular means by which plants respond to stresses. He also has revealed the molecular details of "switches," the promoters of genes, which are responsive to abscisic acid, the plant hormone essential to respond to stress. By making plants that have multiple copies of these switches, Ho can develop plants that can turn on protective genes constantly so that the plants will be even more protected against stresses.

Ultimately, his research could yield crops that are much better at defending themselves against heat, drought, cold and soil salinity -- and lessen the estimated $150 billion lost to environmental stresses in American agriculture each year.

The original gene Ho discovered is called HVA1. He has since discovered a few other similarly protective genes. Collaborating with several academic and industrial labs, he is in the process of making transgenic turf grass and ornamental plants to express the genes conferring higher levels of stress tolerance.

"Plant protection and regulation of seed germination are my major focuses," he said. "It always amazed me that plants, which are immobile, survive under stress better than humans and most mammals do. For example, during St. Louis summers we have temperatures as high as 105 degrees Fahrenheit, and in winter 10 below F. If we were immobile, like plants, we probably would have terrible times surviving were it not for heating or air-conditioning. Trees survive year after year in these conditions, reproduce the next generation, and the next generation survives as well. We want to figure out how plants do this."

Ho was born in Nanking, China, the sixth of seven children, and moved with his family to Taiwan in the wake of the Communist takeover in China. For his college entrance exam, Ho placed in the top 1 percent of all students in the country, qualifying him for medical school, the most popular technological program in Taiwan. Again, Ho went against the grain.

"Because I like plants so much, I waived my chance to go to medical school, which was considered very odd," Ho recalled. "Over the objection of my father, I made the decision to study plants, and that set the direction of my career over the past 30 years."

Today, Ho is in an exciting milieu here. With the establishment of the Danforth Plant Science Center, plant science has never been stronger, and the opportunities for making lasting contributions to agriculture and plant molecular genetics are riper than ever. New biology department chair Ralph Quatrano, Ph.D., the Spencer T. Olin Professor in Arts & Sciences, has made Ho associate chair for space and facilities to meet the challenge of incoming faculty and the burgeoning enrollment of undergraduate biology majors. He is constantly busy with research, collaborating with four graduate students, two post-docs and two undergraduate students. For years he has taught an important introductory biology class, and now he has teaching responsibilities on the subject of plant biochemistry.

The Ho family prepares to board a submarine for undersea exploration during a recent trip to Hawaii.

Challenging times

In his increasingly "spare" spare time, Ho and his wife like to travel. They keep in touch with their daughter, who is now 20 and a junior at MIT pursuing a specialized major in civil engineering and urban development.

He prizes his relationships at the University as well. "We are in exhilarating times in biology at Washington University," he said. "Plant biology is certainly a strong part of our department, but I think our unique feature is that we are diverse, but at the same time highly interactive and cohesive. The many different components do not exclude each other. We all learn something from each other."