Integrated ‘omics’ characterization of conserved nectar production mechanisms using floral and extrafloral eudicot nectaries

Floral and extrafloral nectar, produced by nectaries, is offered as a reward to foster plant-animal mutualisms with pollinators and invertebrate predators. Attraction of pollinators through floral nectar improves fruit set in 87 out of 115 global food crops. Meanwhile extrafloral nectar, reported in 745 genera, attracts invertebrate predators, such as ants, as an indirect defense mechanism to reduce herbivory. Nectar quality (i.e. volume and composition) strongly correlates with the efficiency of these plant-animal mutualistic interactions, yet nectar composition has typically only been defined by targeted analyses of the two most predominant classes of metabolites, carbohydrates and amino acids. Other less abundant components of nectar are often unaccounted (i.e. vitamins, alkaloids, phenolics, terpenoids, lipids, metal ions, hormones, and proteins). Furthermore, molecular understanding of nectar synthesis and secretion is limited to a few reports of genes directly affecting the de novo production or quality of floral nectar. Comprehensive GC-MS based metabolomics techniques capable of quantifying trace components of nectar were used to characterize nectar composition from species, spanning three eudicot families (Cucurbitaceae, Malvaceae, and Solanaceae). This enabled examination of relationships between nectar composition and biological factors such as the sex of the flower, plant-animal mutualisms, and functional role of the nectar regarding plant reproductive success and defense (i.e. floral and extrafloral nectar). These analyses contributed the metabolomics portion of a comprehensive systems network-based project to define the conserved molecular mechanisms of nectar synthesis and secretion among floral and extrafloral nectaries of the core eudicots. Through the analysis of the transcriptomes and proteomes of nectaries from a broad range of phylogenetic plant clades, we identified core sets of genes conserved within eudicots required for nectary synthesis and secretion. These results also supply a foundation for targeted studies of nectar quality improvement, which will benefit pollinator health, promote plant reproductive success, and enhances biological control of crop pests