Plants produce a wide diversity of volatile compounds that facilitate interactions with their environment, ranging from attracting pollinators and seed dispersers to protecting themselves from pathogens, parasites, and herbivores. Recent discoveries have allowed an understanding of how plants produce volatile compounds, but little is known about how volatiles are released from plant cells into the atmosphere. Until recently, it had been assumed that volatiles simply diffuse out of cells. However, simple diffusion cannot occur rapidly enough to prevent accumulation of toxic levels of volatiles in plant cells. Thus, plants must have cellular mechanisms that facilitate the emission of volatiles. This project will characterize the molecular processes involved in the emission of plant volatiles out of the cell for the first time. This research will identify new targets for metabolic engineering for altering either accumulation of compounds, or their release from plants, to improve agronomic/horticultural traits, biofuel production, and crop nutritional value. Beyond plants, chemical communication plays an important role in microbial communities, in the lives of insects and in interactions between animals. How volatile compounds are released from these organisms is a similar open question. The information obtained from this project may enhance understanding of volatile release mechanisms used by other organisms. Since plant volatiles significantly contribute to our environment, the results obtained will provide a foundation for development of more accurate atmospheric volatile emission models.
It has long been accepted that volatile compounds, lipophilic low-molecular-weight molecules with high vapor pressures, simply diffuse out of cells. The recent finding that volatile emission driven solely by diffusion would lead to toxic levels of volatiles in membranes raises new questions about how plant volatiles are released from cells into the atmosphere. This research will employ an integrative strategy comprised of genetics, molecular biology, metabolic profiling, protein and membrane biochemistry, and mathematical modeling of mass transport to (i) characterize ABC transporters participating in export of volatiles across the plasma membrane; (ii) elucidate the role of PhSV2, a homolog of mouse synaptic vesicle protein 2A, as a novel vesicle trafficking protein involved in volatile emission and (iii) determine the effect of cuticle chemical composition and crystallinity on volatile emission. Petunia flowers will be used as a model system since they emit high levels of benzenoid/phenylpropanoid volatiles, have available genomic/transcriptomic resources, and are amenable to genetic manipulations. This work will uncover the biological processes involved in shuttling plant volatiles across the cytosol and plasma membrane. The proposed research will provide multidisciplinary training to undergraduate and graduate students, and postdoctoral researchers. The educational program will also introduce thousands of middle and high school students throughout the U.S. (particularly from rural and underprivileged areas) and abroad to STEM-based research by developing a web-streamed "electronic field trip", with support from Purdue zipTripsTM. The goals are to improve student enthusiasm, interest, and perceptions about scientific careers.
