When Keiko U. Torii was in first grade in Japan, her mother offered to buy her an "elaborate" birthday present, as long as it was related to schoolwork. Torii asked for a telescope and a microscope, but the family could afford only the microscope. "It was a simple one, but I loved it so much," she recalls. She looked at pond water, small bugs, salt crystals—anything she could put on a slide.
These early events opened Torii's passion for observing and trying to understand the world around her. That passion led Torii to her current post as professor of biology at the University of Washington, to a string of groundbreaking papers on the genetics underlying plant development, and to a slew of top awards. The outside recognition is gratifying to Torii, who has become a role model for aspiring women scientists, but it isn't what drives her, she says. "The main reward is discovery. There is a joy that comes from looking at inspiring images and solving the puzzle of the beautiful patterns."
The first big puzzle Torii tackled was how cells communicate to create a plant's characteristic architecture. As a postdoctoral fellow at the University of Tokyo, she studied a stubby mutated form of Arabidopsis, called ERECTA, which has blunt fruits and short leaf stalks. She and colleagues cloned the gene responsible for the plant's short stature. In a landmark 1996 paper published in Plant Cell, they reported that the ERECTA gene coded for a membrane-spanning protein. The part of the protein inside the cell was an enzyme called a kinase, typically used to transmit signals and control complex processes. The portion on the outside of the membrane was a receptor that perceives chemical signals from other cells. The implication: Cells employed such proteins to tell each other what to do. "At the time, it was quite unexpected that plant cells might talk to each other using proteins called receptor kinases to coordinate growth," Torii says.
Torii then had a hunch that plants might have similar, even redundant, protein kinases that look and function like ERECTA. At the time, it was a heretical concept, but she forged ahead and discovered two genes that looked and worked like ERECTA. She created a mutant variety of Arabidopsis by knocking out all three genes and made a discovery, published in Science in 2005, that launched her down a new research path.
The leaves of plants have tiny pores called stomata, each of which is opened and closed by two guard cells. The pores allow carbon dioxide (or oxygen when the plant is respiring) to enter and oxygen and water vapor to exit. The process of making the stomata is "very simple and very beautiful," says Torii. But the mechanism was largely a mystery—until Torii looked at her triple-knockout mutants under the microscope. Instead of seeing stomata spaced at regular intervals as they usually are, she saw that nearly the entire leaf surface, or epidermis, was covered with the pores. "It's not like I had a long-planned scheme to study epidermal patterning, but when I saw the stomata everywhere, my intuition told me this was something to go for," she recalls.
Each stoma develops from its own stem cell, just like a neuron and a muscle fiber in the human body. The mechanism for making and differentiating a stomatal stem cell was unknown. Torii's simple visual genetic screen using a microscope led to the discovery of two proteins, MUTE and SPEECHLESS, published in 2007 in the journal Nature. These proteins switch on gene expression programs to initiate and differentiate stomatal stem cells together with other proteins, which Torii named SCREAM. Surprisingly, the proteins Torii identified are of the same class as the master regulatory proteins for neuron and muscle development. "It is intriguing that plant and animal cells use a similar developmental logic to make specialized cells," she says.
Together with collaborators, Torii recently found a small peptide that cells emit to communicate with their neighbors, which act through receptors like ERECTA. Torii's lab is now developing protocols for live cell imaging and engaging in cross-disciplinary collaborations with material scientists to chart the regulatory dynamics and signaling pathways cells use to create the stomatal patterns. "We are very excited about our collaboration with other disciplines to further our understanding of how plants develop," Torii says.
Her work is not only rewriting the textbooks on plant development, it also could have practical implications. Plants adjust the number of stomata in response to drought and other environmental conditions. So understanding the underlying process should help predict how well crops, trees, and other plants can cope with climate change and other threats.
Torii looks back wistfully on the time years ago when she played the violin semiprofessionally at weddings and other events. "Now, all my nonscientific time is devoted to my children, who are seven and four," she says. Fortunately, her husband, a theoretical physicist, is often on hand to look after the kids when she needs to rush to the lab to solve a problem—and lately she's even been able to pick up the violin again to play along with her daughters. It's evident that her passion for observing the natural world still runs deep. "My best time is sitting at a microscope and looking at plant cells," she says.