Harvard, California Researchers Discover Spur Development Gene in Columbine

Researchers at Harvard, California State University, Sacramento, and University of California, Santa Barbara, discovered a new gene responsible for nectar spur development in columbine flowers, according to a study published in the Proceedings of the National Academy of Sciences in September.

Study co-author and basketball fan Evangeline S. Ballerini said she named the gene POPOVICH — POP, for short — after Gregg Popovich, head coach and president of the San Antonio Spurs.

“I’m a nerdy scientist and a sports fan. I wanted to play off of the San Antonio Spurs and the columbine spurs,” Ballerini said.

Much like a coach directs players, POP directs nectar spur development in columbine flowers and is essential to promoting biodiversity, according to Ballerini.

Ballerini — who currently serves as an assistant biology professor at CSU Sacramento — co-authored the study with Organismic and Evolutionary Biology professor Elena M. Kramer, UCSB biology professor Scott A. Hodges, and Harvard graduate students Molly B. Edwards and Ya Min.

The discovery was the result of a cross-country collaboration between Ballerini, her Ph.D. dissertation advisor Kramer, and her postdoctoral fellowship mentor Hodges.

Hodges said he has embarked on a “lifelong quest” to map out the relationships between columbine flowers and related species. He added that the Aquilegia genus, to which columbine flowers belong, is unique because it has achieved incredible diversity in a relatively short period of time, with minimal genetic variance between species.

Rapid speciation in columbine flowers is due in large part to nectar spurs, which allow the flowers to attract different pollinators and eventually become reproductively isolated with little genetic change.

“The big picture question is just how has diversity on the planet evolved, and this is a good system to address those questions,” Ballerini said.

After working in Kramer’s lab, Ballerini joined Hodges on some of his evolutionary biology projects with columbine flowers at UCSB.

When Ballerini crossed a spurred columbine species with the only spurless columbine species, she was able to identify a region of 1000 individual genes associated with spur development.

To narrow down this list of genes, she conducted another experiment where she crossed four different columbine species. Ballerini compared these results with a prior dataset from Min that studied the expression of genes in early spur development.

Cross analysis of the two datasets allowed Ballerini to identify eight common genes, among which only one, POP, was expressed in the quantitative trait locus, suggesting a connection between the gene and the absence of spurs in the spurless species.

The researchers said they are hopeful their discovery will help them further map out the evolution and development of nectar spurs.

“To get a complete picture of how spurs evolve, we need to know the players of what we call upstream and downstream of POP,” Hodges said, adding that further research is needed to identify which genes POP controls as well as which genes control POP.

“We can then start asking even further questions about all those other groups of plants that independently evolved spurs. How did they do it?” Hodges said.

POP also opens up developmental biology questions about its function.

“We have shown that POP is necessary for spur development, but we have not yet proven that POP is sufficient for spur development,” Kramer said. “Is it what we might call a master regulatory gene for spur development?”

Ballerini said the culmination of this project was particularly rewarding, given her longtime “dream” of discovering a novel gene.

“When I was an undergrad and I first was learning about genetics and evolution, I had this dream of ‘Oh, you could identify genes that are really important for evolution,’” Ballerini said. “It took a while but, in a way, in this paper I’m sort of fulfilling my undergrad dreams.”

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