An organ known as the floral nectary is responsible for producing nectar in many plant families. Despite its central role in plant pollination, very little is known about the molecular mechanisms of nectar synthesis and secretion. Indeed, no genes have been shown to directly affect the production or quality of floral nectar. The overall goal of this project is to identify key genes and cellular processes required for nectar production in the agriculturally important Brassicaceae family. In previous studies, seventy genes from the model plant Arabidopsis thaliana were shown to be expressed at greater than 10-fold higher levels in nectaries than in all other tissues examined. The roles these genes play in nectar production will be systematically examined in both Arabidopsis and Brassica rapa (oilseed rape) through gene knockout and overexpression studies. Mutant plants will be subjected to thorough phenotypic characterization that includes evaluation of nectary morphology and ultrastructure, global changes in gene expression within nectaries, and overall impacts on nectar volume and composition. It is expected that these studies will provide new insight into the genes and pathways required for nectar production in plants.
BROADER IMPACTS Determining the molecular basis of nectar production can have enormous impacts on U.S. agriculture, ranging from increasing yields in a wide range of pollinator-dependent crop species to targeted improvements of apiculture. Each year approximately 1.5 million acres of Brassica rapa and related oilseed crops are planted in the U.S. alone. Significantly, B. rapa is almost entirely dependent on the efficient attraction of pollinators to achieve maximal yields. Indeed, poor pollinator visitation can cut yields of Brassica oilseed, as well as unrelated crop species, in half. The long term goals of this project are to elucidate the underlying mechanisms of nectar production in the agriculturally important Brassicaceae family, and how this understanding can be translated into higher yields in multiple crop species. In addition, this project will provide significant research experiences and educational opportunities to a large number of undergraduate students at the University of Minnesota - Duluth, a primarily undergraduate institution. A detailed description and results derived from this project can be readily viewed at www.d.umn.edu/~cjcarter/carterlab.html. Microarray data will be deposited at GEO, gene annotations at TAIR, and metabolomics data will be integrated into the metabolomics database developed at Iowa State University (www.plantmetabolomics.org). Seed stocks will be available through the project and through the ABRC (www.biosci.ohio-state.edu/pcmb/Facilities/abrc/index.html).
Nearly 90% of all flowering plants produce nectar in order to attract pollinators, including one-third of all crop species. Indeed, U.S. pollinator-dependent crops have an estimated annual value of $25 billion. In spite of its central importance in plant-pollinator interactions, the genetic and molecular mechanisms underlying nectar secretion were largely unknown until the present work. Specifically, during the grant period nearly 300 genes were identified that are active only in the nectaries of the Brassicaceae family (nectaries are the floral glands that secrete nectar). The Brassicaceae family includes crop plants such as cauliflower, broccoli, cabbage, turnip, and canola. The roles and molecular functions of nearly 200 of these genes in nectar production were subsequently evaluated. Of these, seventeen genes were found to impact nectary function. The specific roles of these genes in nectar production were found to include sugar metabolism, sugar transport, transcriptional regulation, and hormone metabolism and response, along with six genes of uncertain activity. Perhaps more importantly, the results of this work indicate the mechanisms of nectar production may be shared by many plant species, suggesting the results are widely applicable in terms of the potential for crop improvement. Thus far, this work has resulted in seven recent peer-reviewed publications, with three more in preparation. More broadly, understanding the genetic and molecular mechanisms controlling nectar production, as well as plant-animal interactions mediated by specific nectar components, now allows targeted studies to improve overall pollination efficiency in multiple plant species, and have the potential to greatly impact apiculture. For example, an increase in nectar production is known to result in a concomitant increase in pollinator visitation, pollination efficiency, and yield, even for highly selfing plant species. Crop species with stably enhanced levels of nectar production are now being developed and will be evaluated for their ability to impact pollinator visitation and yield. Finally, five graduate students and 15 undergraduates have been supported through this project, with eight of the undergraduates authoring or co-authoring published manuscripts. These students also presented eight posters at national meetings. Major results from this project are publicly available at www.nectarygenomics.org.
