Abstract of NSF Award

Nearly 90% of flowering plants produce floral nectar, the volume and composition of which have been correlated with the efficiency of animal-mediated pollination that impacts the production of 87 out of 115 (~76%) of the leading global food crops which represents an annual value of $29 billion in the U.S. alone and accounts for one-third of total food production. Although sugars are the predominant nectar solutes, ~10% of nectar dry weight is represented by many types of non-sugar solutes, including specialized metabolites, like pigments. Pigments play essential roles in biotic interactions throughout the Tree of Life, with natural pigments having a global market value of >$5B annually. This project will use a comparative genomics interdisciplinary approach to test the central hypothesis that colored nectars contain novel and known pigments, which evolved from being selectively favored through having spectral qualities attuned to pollinator vision. The activities outlined in this study are wholly novel and will provide new insights into the biology of an essential plant-animal mutualism on a genome-wide scale by (1) systematically profiling nectar pigments across species; (2) determining to what extent nectaries can actively control non-sugar nectar content, with an emphasis on nectar pigments; (3) understanding how evolutionary and natural history impact nectar quality with respect to pigment content; (4) identifying and characterizing enzymes involved in pigment synthesis; and, (5) systematically evaluating the true biological functions of nectar pigments. With respect to broader impacts, the project will help train the next generation of plant biologists by providing research training experiences for undergraduate, graduate, and middle school students. In addition, the project will take advantage of the broad public interest in the conservation of plant-pollinator interactions through citizen science projects.

Plant-pollinator interactions have at least partially driven the massive species radiation observed in the angiosperms, leading not only to extreme diversification in flower size and morphology, but also the accompanying chemistries behind attractants (color and scent) and rewards (nectar and pollen). Although rare, one floral trait that has evolved multiple times is colored nectar, which is suggested to serve as a visual cue of reward to prospective pollinators. Approximately 70 plant species are known to produce colored nectars, but the identities of these pigments, their associated syntheses, and true biological functions, have not yet been described. To address this gap in knowledge, the overarching goal of this project is to decipher the diversity, synthesis, and function of nectar pigments within a phylogenetic and evolutionary framework. The specific aims of this project include:

1) Systematic identification of nectar pigments in 20+ taxa of diverse lineages via LC MS/MS, including multiple sister taxa with different colored nectars.

2) Comparative transcriptomics and proteomics of nectaries and nectars. RNA-seq will be conducted on nectaries throughout floral maturation to enable comparative mining of pigment synthesis pathways, as well as nectar protein identification, which we predict to be involved in pigment formation.

3) Determine mechanisms of pigment formation. This aim will characterize the role of nectar proteins in pigment formation.

4) Initiation of functional analyses of nectar pigments. Nectar pigments may serve as visual cues to pollinators. This aim will evaluate if colored nectars are visible and conspicuous to suspected pollinators.

All methods and datasets will be made publicly available through the project website (www.nectarygenomics.org) and publications. Long-term access will be provided through established public data repositories.