Abstract
Plants have evolved different mechanisms to attract pollinators and promote outcrossing. One of these mechanisms is the production of floral nectar, a sweet liquid composed of carbohydrates, water, amino acids, and secondary metabolites. Across flowering plants, variation in these components has evolved in response to selection pressures exerted by different animal pollinators. The genetic causes of nectar variation are not well understood. Prior studies have largely concentrated on specific genes involved in nectar production with very few assessing entire genetic pathways involved in nectar production and secretion. Here, I used comparative transcriptomics to explore the genetic pathways involved with nectary development, nectar production, and nectar variation in four related species of Aquilegia with different animal pollinators across a developmental series. Gene expression patterns in all four taxa suggest that at earlier stages in nectary development, starch is synthesized in preparation for nectar secretion. Just prior to nectar secretion, genes involved in sugar biosynthesis are upregulated. Interestingly, at the time of nectar secretion, genes in auxin response and programmed cell death are upregulated, indicating that they may be involved in the holocrine mechanism of nectar secretion in Aquilegia. Measurements of nectar concentration in the taxa explored indicate that pollinator type influences this trait. Genes involved in the synthesis of secondary metabolites such as TERPENE SYTHASEs and CINNAMYL ALCOHOL DEHYDROGENASE, among others, were differentially expressed in specific taxa during nectar secretion and may contribute to variation in nectar composition between species with different pollinators. This project began to uncover the genetic underpinnings of nectar biology in Aquilegia and provides a solid foundation for future exploration of nectar evolution and adaptation.