Comparative Functional Genomics of Nectaries and Nectar in the Dicots

One-third of all crop species produce floral nectar and are dependent on animals for reproduction. Moreover, crops such as cotton, bean, pea, apple, cherry, peach, and blueberry, all produce extrafloral nectar to attract mutualistic predatory insects, which protect plants from herbivores. U.S. pollinator-dependent crops alone have an annual value of nearly $25 billion, and extrafloral nectar represents one of the few defense mechanisms for which stable effects on plant health and fitness have been demonstrated. This project will employ genomics technologies to study the molecular mechanisms involved in the synthesis and secretion of nectar components across species and nectary types. If successful, this project will provide significant new insight into these processes and the plant-animal interactions mediated by specific nectar components that will allow targeted studies to improve overall pollination efficiency, enhance biological control of pests that attack crops, and have the potential to greatly impact apiculture. With regard to outreach and training, the project will provide interdisciplinary research training for students and postdoctoral associates. Project graduate students at Iowa State University will also serve as GK12 Fellows in GK12 Symbi program (http://www.gk12.iastate.edu/). Supported by NSF, the Symbi program is a partnership between ISU and middle schools and high schools that serve primarily under-represented students in the Des Moines Public School District. GK12 Fellows will serve as "resident scientists" who will work with teachers to develop innovative, hands-on and engaging science activities for select middle school or high school science students. Finally, the project will also provide research experiences for high school students from Cornell High School (Cornell, Wisconsin).



The central hypothesis driving the project is that the genetic programs underlying nectar synthesis, secretion and function are at least partially conserved between diverse species and nectary types. To address this hypothesis, the project will apply comparative genomics approaches to the characterization of the (i) synthesis, (ii) secretion and (iii) biological function of nectar components across a diverse set of core eudicots, including Brassica sp., cotton, tobacco, squash, Lima bean, and acacia. The specific objectives and approaches include:

1. Comparative expression profiling of nectaries throughout the secretory process. Both the floral and extrafloral nectary transcriptomes and proteomes of the respective species will be examined at several time points throughout the secretory process;

2. Comparative metabolomics of nectars. Nectar metabolites will be comprehensively characterized through a non-biased GC-GC/MS-MS and LC/MS-MS approach;

3. Comparative and functional analysis of nectar proteins. Specific arrays of proteins have been reported in several nectars, which confer both protective and attractive properties. Thus, the proteomes of both floral and extrafloral nectars will be defined and functionally characterized across species.; and,

4. Informatics, database building & initiation of mechanistic studies. Mining of global expression data from actively secreting vs. inactive nectaries will allow the identification of genes and cellular processes central to the basal pathways for active nectar secretion across species. Metabolomic data will be linked to activities identified from expression data to assess their impacts on nectar production and composition.

All validated data will subsequently be integrated into an existing public online database (www.nectarygenomics.org), with subsets of data also being made available to the public at the National Center for Biotechnology Information (http://www.ncbi.nlm.nih.gov/) and the iPlant Collaborative (www.iplantcollaborative.org).