Xuemei Chen finds beauty in cellular organization and seeks to understand the minute, discrete steps through which different types of plant cells acquire their fates. When pressed to examine the events that determined her own fate, however, she concludes that she landed on her path of studying plant biology largely by serendipity.
Growing up in the Hei Long Jiang (Black Dragon River) province in northeast China, Chen had limited options, but she did her best to take advantage of the ones she had. Even in high school, she knew she wanted to study biology. But Beijing University allowed the province to send only two biology majors—one in biochemistry and one in plant physiology. Selection was determined by student scores on the country's entrance exam.
"I knew I did pretty well, but I didn't know if I was number one. What if someone else did better than I did and we both applied for the same subjects?" Chen says. Thinking the subject would be less competitive, she chose plant physiology and was accepted. "It turns out that the other student who got in had exactly the same test score I did. To this day, I often wonder what would have happened if we'd both applied to biochemistry."
One year into her studies at Beijing University, she was allowed to shift to a different major, but plants held her interest. Once she completed her degree, she went to Cornell for her graduate work, where she studied the genetic control of chloroplasts—the cellular organelles where photosynthesis takes place—and has since been hooked on gene regulation. Now, Chen studies plants at both the molecular and the genetic levels and the more she discovers, the more excited she gets. "Sometimes, when I come up with an exciting hypothesis, I can't sleep for days," she says. "It's all just so interesting—I want to know how these molecules in the cell organize the cell, and then eventually the whole organism."
In her lab at the University of California, Riverside, Chen's research has two major foci. At the developmental level, she's studying stem cells that give rise to flowers that, unlike the shoot stem cells that continue to produce biomass as long as a plant is alive, cease to be stem cells once all floral organs are made. "If you understand how floral stem cells are regulated, you could take advantage of them to generate biomass. You could change the size of the fruit or the number of the seeds," she says. "Right now we're just trying to understand the basic mechanisms underlying stem cell regulation."
She hopes to get a better idea of how undifferentiated cells acquire their fates and is unraveling the specific steps that transform stem cells into a flower's petals, sepals, stamens, and pistil. She has discovered that the genes controlling these patterns can be controlled through mechanisms that limit protein production after a gene has been transcribed into RNA—a surprise to plant biologists, who previously thought floral development was controlled entirely by regulating gene transcription. She's now building on this discovery, studying Arabidopsis mutants that never stop making floral organs.
Chen's second line of research focuses on small RNAs. In 2002, her lab and two others were the first to find that microRNAs—regulatory molecules first identified in the roundworm—existed in plants. The microRNAs Chen described play an important role in floral patterning and gene silencing, and she's now looking deeper to gain a better understanding of how they're made and how they work.
MicroRNAs can act in two ways to regulate a target gene, either eliminating its messenger RNA or inhibiting it so it can't be transcribed into proteins. The inhibition aspect is still poorly understood, and that's where Chen is focusing her efforts. Her discoveries in plants, including the identification of an enzyme that helps stabilize microRNAs and a separate protein that helps drive their creation, have frequently been followed by parallel findings—in her lab and others—demonstrating that the same mechanisms also exist in animal cells. "Once you figure out how these small RNAs work, you could harness their power to target specific genes, silencing them so as to help agriculture or treat human disease," she says.