Within a cell there are thousands of complex biochemical interactions, many of which are mediated by very specific enzymes. The evolution of complex biochemical interactions could follow a stepwise process, with each new elaboration of an enzyme being optimized by natural selection. However, very little is known about how these complex interactions have evolved and what evolutionary forces shape them. By examining the changing structures of an enzyme within the context of the phylogenetic tree of the organisms that have the different forms, one can trace the evolutionary history of a novel biochemical pathway and determine when a particular functional elaboration took place. Specifically, it is possible to use the variations in the present-day biochemical pathway to infer the DNA sequence underlying the extinct ancestral pathway. The DNA information can be used to infer the ancestral pathway and thus determine its function and understand how evolution acted on it to create the current pathway. Using plants of the family Brassicaceae (which includes crops like broccoli, cabbage, and canola), the PIs will examine the evolution of the biochemical pathway for forming a chemical that is crucial to deterring herbivores.
This grant will also support the graduate student's outreach work at local elementary schools and the mentoring of 8th grade girls. International collaborations will be strengthened during this research. Finally, the anti-herbivore compounds made by this biochemical pathway are thought to play a role in cancer prevention, so the basic research described here could have medical as well as agricultural importance.
Understanding how plants evolve new defense mechanisms To defend themselves against insect herbivores many plants synthesize a variety of toxic chemicals. However, the insects are evolving too, and the plants need to keep up with the diverse and ever-changing community of herbivores by changing the arsenal of chemical they use to defend themselves. This study investigates the evolution of a novel anti-herbivory compound found in the plant family Brassicaceae. Members of this family, known as mustards, include important crops like broccoli, cabbage and canola; they also include the lab rat of the plant world, Arabidopsis thaliana. This project focused on the evolution of a novel set of compounds in the close relatives of Arabidopsis, called Boechera stricta, that grow in the western United States. Northern populations experience selection to use a novel anti-herbivory compound that is not used in the southern part of the range of B. stricta. By determining the evolutionary history of the gene involved in the synthesis of the novel compound we were able to time, in an evolutionary sense, when the new compound arose. We then identified the specific mutations in the gene that changed the function from the old to the new compound found in the northern range of B. stricta. Surprisingly, two mutations were found that can change the function of the gene, with either mutation substantially moving the function towards the novel compounds. These results have important implications for the evolution of new function implying that evolution is not constrained by having to wait for many mutation to get a new, adaptive function. In addition to the impact of these findings on the field of evolutionary genetics, these results were shared with the general public in outreach programs directed towards at-risk and underrepresented middle school students. Students were given tours of the laboratory and participated in activities related to this research project.
