The evolution of function in plant secondary metabolites

For the past 40 years, the ecology and evolution of plant secondary metabolites have been major foci of investigation. We use one class of secondary metabolites, the terpenes, as a case study for exploring the factors regulating the evolution of metabolite function. Evolution of function can occur as a result of change at any of several scales of biological organization. Changes in gene sequence and/or genetic architecture underlie several important evolutionary changes in function, and changes in gene regulation that alter terpene quantities also are linked with functional shifts. In addition, changes in the spatial distribution of terpenes within plants and in the structures used for terpene storage can be involved with functional shifts. Finally, as volatile compounds, terpenes play important roles as signaling compounds, and evolution of function can occur through changes in organisms that receive signals as well as the organisms that send them. In terpenes, significant changes in function have occurred as insects have learned to use terpenes as attractant or deterrent cues. A complete understanding of the evolution of function in secondary metabolites requires studying the regulation of function across all of these scales.