Genetic pathfinder stops to smell the flowers

Plant biologist Kramer studies the staminodia, an illuminating and ‘very strange phenomenon’

By Grace Tiao

FAS Communications

Tucked into a secluded crook of Harvard’s Biological Laboratories building, the office of Professor Elena Kramer betrays a tidiness of mind that can be measured, volume by volume, in the shelves lining the wall. Years of back issues of the journal Science are neatly ordered in cardboard magazine holders and labeled by date. A framed botanical print of a flowering plant hangs nearby, and even that is an exemplary specimen, carefully colored and drawn to scale, its leaves displayed neatly like the limbs of an animal being arranged for the dissection tray.

Kramer, a plant biologist and newly appointed professor of organismic and evolutionary biology, began her career working on animal specimens as an undergraduate at Brandeis University, but she hasn’t left the dissection tray far behind. Her current research focuses on the developmental genetic pathways that regulate flower organ differentiation, and while she works with these plant genes on the molecular level, the research also requires the dissection of live specimens.

Living plants express the genes involved in their developmental pathways through the morphology, or physical structure, of their flowering organs. These typically take on four differentiated forms, known as the petal, carpel, sepal, and stamen — although, on occasion, they independently evolve a fifth category of extra organs called the ‘staminodia.’ It is this fifth category, the extra bells and whistles evolved in unusual blossoms, that interests Kramer most.

“From a genetic standpoint,” says Kramer, “staminodia are a very strange phenomenon. In plant biology, the canonical model of plant genetics accounts for simply four types of organs. It doesn’t give an obvious mechanism for producing more than four types of organs. So how does a plant manage to do that? How can it intercalate something else into a broadly conserved genetic sequence to make a new kind of organ?”

Kramer studies the staminodia of one plant genus in particular: Aquilegia, the family of flowers commonly known as columbines. In addition to having staminodia, which are positioned between the stamens and carpels, Aquilegia has nectar spurs on its petals, with specific forms evolved to accommodate the access of particular pollinators. Aquilegia has undergone a recent adaptive radiation as a genus: 60 to 70 different species with varying kinds of flowers have evolved over the past 10 million to 12 million years — an astonishingly rapid rate of speciation.

“When rapid adaptation happens,” says Kramer, “it can help facilitate the identification of genes that were under selection during different aspects of the radiation. Because it happened so recently, the new species are so closely related that they’re highly interfertile, meaning they can be crossed. If you can cross a plant, you can do genetics with it. In the end, all these characteristics of Aquilegia work together to help us identify the genes that were important for altering the spur length or the color of the petals. That, in turn, helps us understand how developmental genetic pathways work on a general level. How did changes in those genes and functions contribute to the diversification of all flowering plants on a large-scale evolutionary timeline?”

That brand of ambitious inquiry — the generous, sweeping sketching of questions — is surprising in someone who works like a miniaturist painter at her research. Kramer herself admits that the appeal of studying plants for her is the detailed, contained, thoroughgoing nature of the research.

“Plants have such a different way of building their bodies than animals,” she says. “When you study the development of an animal, you usually study it from conception to some kind of birth or hatching, and then it goes off and does what it does as an adult. But plants are constantly building their bodies, and the way they do it is by repeating the same basic modular genetic program over and over again. The modularity means that the program is expressed slightly differently when the plant is making a different kind of organ — like the flower.

“This means that when you study genes that function only during flower development, you can knock out genes that have to do with flower development in your experiments and still have a functioning rest of the plant. Plants have the potential of allowing you to entirely dissect one aspect of their developmental genetic pathway without completely ruining the whole system.”

Dissecting plants — both physically and metaphorically — requires living material, and from March to May, Kramer can be found at the Arnold Arboretum every other week collecting the live specimens she’ll need for her experiments. Even these pleasure excursions (“I’ll pick a nice day of the week to go,” she confesses) are exercises in method and orderliness.

“You have to be organized and know when things are coming out before they all go away,” Kramer says. “The spring ephemerals leaf out early before everything else starts to stir, since they tend to be understory plants.”

For all her organization and botanical expertise, Kramer doesn’t have a garden of her own. She completed her Ph.D. at Yale and almost immediately moved to Harvard’s Department of Organismic and Evolutionary Biology to help establish and grow its plant biology division — and there was never any opportunity to plot out a flower patch of her own.

As she points out, “There isn’t very much land available in the Boston area. That’s why you see so much plant biology research concentrated in the land-grant universities — state schools and places like Cornell. Harvard has exceptional resources, but they tend to be concentrated in the area of plant diversity. I grew up doing lots of gardening in Ohio and had the space. Since I went to college, I’ve never lived anywhere with enough space.”

She points to her desktop computer screen: it’s a photograph of her dog, a shaggy, sandy-haired creature, lying on an immense and perfectly clipped lawn. “I take him with me to the Arboretum on my trips. That’s definitely not my front yard!”