Collaborative Research: The Aquilegia Petal as a Model for the Elaboration and Evolution of Organ Shape

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The body of a plant is made of just a few repeatedly produced structures, such as leaves and stems. However, these structures can vary tremendously in their shape both within an individual and between different species in predictable, consistent ways. This variation in shape is controlled by a combination of cell division and cell shape, which in turn must be controlled by variation in gene expression. The proposed research seeks to determine how complex shapes arise through development and the genes that control these processes. Thus this research will address the fundamental question of how organisms achieve the shapes of their bodies, which is critical to their survival. This research will also have broader impacts through the training of young scientists including undergraduates, graduate students and postdoctoral fellows with outreach efforts to recruit female and underrepresented minorities. The nectar spur of Aquilegia is a complex three-dimensional structure that is recently derived and highly variable among species and, thus, can serve as a powerful model for investigating the control and evolution of complex organ shape. Nectar spurs develop via an early phase of localized, oriented cell divisions that create the prepatterned spur cup, which is then followed by a period of highly anisotopic cell elongation that gives rise to the final length and shape of the spur. Among the closely related and interfertile species of Aquilegia, variation in spur length and shape is generated by changing several developmental parameters: length is primarily controlled by cell anisotropy, which is in turn controlled by the duration of cell elongation; curvature is generated by varying cell elongation between the distal vs. proximal compartments of the spur; and circumference is controlled both by changes in cell anisotropy and cell number in the radial orientation. Thus, understanding the development and evolution of Aquilegia spurs will provide insight into all of these fundamental aspects of lateral organ development, which can provide new perspectives on the evolution of lateral organs more broadly across the angiosperms. The proposed research seeks to integrate multiple lines of study drawn from the fields of developmental genetics, evolutionary genomics/genetics, and biophysics. Specifically, the project will elucidate the fundamental genetic control of petal spur development, explore the roles of hormonal signaling and biomechanical strain in controlling spur development, use QTL-based approaches to identify the genes involved in the diversification of spur shape and use comparative genomic approaches to identify selective sweeps associated with the origin of nectar spurs.