Growing her own answers

4 min read

Hybrid problems provide window to evolutionary change

It was the sick-looking plants that intrigued Kirsten Bomblies as she worked on plant genetics at the Max Planck Institute for Developmental Biology over the past few years.

The plants were stunted and yellow with shriveled leaves. Their immune systems were in high gear, but they hadn’t been attacked by a pathogen or pest.  They were born that way.

Bomblies, a plant geneticist and molecular biologist, tracked the condition to a kind of plant autoimmunity, where the plants’ internal defenses, originally intended to fight external pests, fungi, and bacteria, were switched on and instead attacked the plants’ own tissues.

The condition, called hybrid necrosis, has long been known to affect crosses of different plant varieties, or hybrids. Bomblies and her colleagues were the first scientists since a disregarded 1929 report to track the problem to plant immune responses. They were also the first to clone the genes involved.

In July, Bomblies brought her studies from Max Planck, where she was a postdoctoral fellow in the lab of Detlef Weigel, to Harvard, where she began work as an assistant professor of organismic and evolutionary biology. Bomblies received her doctorate from the University of Wisconsin, Madison, in 2004 and last fall won a prestigious MacArthur Foundation Fellowship, a $500,000 no-strings-attached grant given annually to creative, original individuals who the foundation judges have the potential to make important contributions to society.

Bomblies believes the relationship between hybrid necrosis and plant immunity is a result of the evolutionary divergence of different varieties of the plant involved in the study, Arabidopsis thaliana, an unassuming member of the mustard family that has become a favorite study subject of plant geneticists. In pursuit of what the plant could tell her about the roots of genetic diversity, Bomblies crossed many different strains of Arabidopsis and studied the hybrid plants that resulted.

“We did a screen to see how many of them would be normal and how many would have problems. We found that 2 percent had very severe problems,” Bomblies said. “It turns out that’s from massive amounts of cell death. The tissue just dies off. These plants are just completely overactivating their immune systems.”

Because immune genes are forced to rapidly evolve to keep pace with the constant onslaught of bacteria, viruses, fungi, and pests, Bomblies believes the hybrid necrosis results from the large diversity among Arabidopsis immune genes. Since one hallmark of different species is their inability to reproduce with each other, the findings may highlight one mechanism through whichArabidopsis thaliana varieties evolve into different Arabidopsis species.

“It’s kind of a model for some of the earliest events happening in population divergence. I can’t say any will speciate, but it’s an interesting model,” Bomblies said.

Bomblies wants to continue to study the phenomenon at the molecular level and to investigate how temperature affects it. Plant immune systems become less responsive as temperature increases beyond its normal environmental range.

Bomblies is also interested in investigating another type of Arabidopsis diversity, that of Arabidopsis arenosa, known to grow under widely differing environmental conditions.

Seventy join Harvard faculty for 2009-10

Assistant Professor of Organismic and Evolutionary Biology Kirsten Bomblies is among 70 new faculty members who are joining the University’s various Schools this year. With the start of the new year, Harvard has hired 41 new assistant professors, six associate professors, and 23 new full professors, and promoted 20 existing faculty members to tenured professor positions.

The Office of Faculty Development and Diversity (FD&D) serves as Harvard’s central faculty affairs office and has launched a new Web site designed to support Harvard’s mission to find, develop, promote, and retain the world’s best scholars. The site provides information related to faculty recruitment, resources designed to support faculty teaching and scholarship, and detailed descriptions of institutional policies, benefits, and services.

The site will also serve as a vehicle to introduce faculty to the broader Harvard community and the public. The Web site’s home page will provide links to this year’s new faculty on a rotating basis.

Working closely with colleagues across the University, FD&D oversees and guides institutional policies and practices in all areas of faculty affairs, providing intellectual leadership and coordination across Harvard’s Schools.

To view detailed profiles of some of Harvard’s newest faculty members or to learn about the Office of Faculty Development and Diversity, please go to