Developmental Biology, Plant Biology
National University of Mar del Plata
Dr. Pagnussat is an adjunct researcher of the National Scientific and Technical Research Council of Argentina at the Institute of Biological Research, National University of Mar del Plata, Argentina.
Dissecting Cell Signaling Networks During Embryo Sac Development and Fertilization in Arabidopsis thaliana
Growing up in Mar del Plata, a city on the Atlantic coast of Argentina, Gabriela Pagnussat became fascinated by the world around her at an early age. She observed bugs, studied flowers, and loved to go on field trips with her classmates. She conducted rudimentary experiments to see how different substances interacted—sand, sea water, algae, and mud were all under her scrutiny. But it was a genetics class in her senior year of high school that made her realize biological research was her calling.
“In college, I imagined myself working with animals and doing research more focused in biomedicine,” says Pagnussat. “It wasn’t until I took a course about plant biochemistry and physiology that I became very interested in plants.”
Pagnussat grew fascinated with how plants respond to tiny changes in their environment by using hormones to regulate their cellular processes. After receiving a bachelor’s degree in biology, she stayed at the National University of Mar del Plata for a Ph.D. in plant biology. Later, during postdoctoral fellowships in Argentina and at the University of California, Davis, Pagnussat focused on auxin, a hormone that plays important roles during the plant life cycle, and its interaction with the chemical nitric oxide.
Scientists knew that nitric oxide is key to the communication between blood vessels and surrounding muscles in animals. But Pagnussat’s work revealed the chemical’s role as a signal molecule in plant root development. Nitric oxide allows plants to grow roots, a process triggered by auxin. Perhaps more important is the hormone’s involvement in plants’ reproduction, revealed during Pagnussat’s postdoctoral fellowship at the University of California, Davis. Plants create two forms of reproductive cells to pass along their genetic material—male cells that form within pollen grains and female cells that grow in an embryo sac within an ovule, the female sexual structure of plants. Auxin is produced at one end of the embryo sac, which contains just eight cells. If all goes according to plan, one of these cells becomes an egg, with the others playing supporting roles.
However, as Pagnussat’s postdoctoral studies revealed, each of these eight cells is exposed to different levels of auxin while it is growing inside the embryo sac. The amount of exposure determines whether it becomes an egg cell or a supporting cell. If auxin levels are altered, more than one egg cell may form, affecting the entire ovule fertility.
“This was the first evidence that early cell fate in the embryo sac relies on positional information,” Pagnussat says. It was also the first report of a plant hormone acting as a morphogen—a compound that affects development according to its concentration.
Throughout her postdoctoral work, Pagnussat didn’t just shed light on the role of auxin. She also characterized 130 mutations that cause dysfunctional reproductive cells in plants. While analyzing these mutations, she noticed that many of them were in genes known to be involved in regulating reactive oxygen species (ROS), molecules that can damage cells.
Pagnussat returned to Argentina at the Institute of Biological Research in the National University of Mar del Plata for a faculty post at her alma mater, where she continues to probe the link between ROS-related genes and reproductive cells. During the formation of an embryo sac or an ovule, certain cells must self-destruct at key times in development, allowing for the growth and division of only specific cell types. Pagnussat suspects that auxin, ROS molecules, and cell death play an integral and complementary role in embryo sac development and fertilization.
Her research is revealing the molecular underpinning of how cells precisely regulate these processes, but the findings could have broader implications. All sexually reproducing organisms must control the varying fates of different groups of cells, and other organisms could share the mechanisms that plants use.
The fascination with the world that Pagnussat felt as a child has increased over the years, she says, inspiring more questions and new directions for her research. “I feel that it is a privilege to be a scientist, it’s never the same, and I think I will never get tired of it.”