The Downside of Smelling for Danger: Fitness Costs of Plant Defense Priming via Plant-Plant Volatile Signaling

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Plants can detect airborne chemicals in their environment that are indicative of impending stress and prepare defenses prior to experiencing the stress. This phenomenon has been termed "priming". This project explores the molecular patterns of response indicative of priming using both field observations and controlled environment experiments. Since ecological theory predicts that there should be a cost to priming, measurements of the effects of priming on plant growth, reproduction and rates of herbivory will be used to determine both the costs and benefits of priming. Finally, the progeny of primed and non-primed plants will be examined to determine if the offspring of primed plants are better defended than offspring from non-primed plants. This project will continue the "Million Leaf Project", which is a science workshop developed by the lead investigator to introduce citizens and grade school students to plant-insect interactions by teaching an experiential approach to both measure and analyze the damage experienced by plants and their leaves. Participants collect their own data to explore how much pressure insect consumers put on plants, and therefore how plant chemical defenses and sensory perception might have evolved. The results of this research may also be applied to inducing greater resistance to herbivory in agricultural crops, thereby reducing losses to pests.The principle objective of this study is to test fitness costs and molecular patterns associated with defense priming under controlled and field conditions in two phylogenetically disparate Rosids: Arabidopsis thaliana and Phaseolus lunatus. Overwhelming evidence exists that plants respond to certain volatile organic compounds (VOCs) such as herbivore-induced plant volatiles (HIPVs) from their neighbors or distal parts of themselves by "priming" (i.e., preparing) their defenses. However, the volatile-associated molecular patterns (VAMPs) indicative of priming are not well known. Moreover, ecological theory predicts that induced processes should incur fitness costs, but there is currently limited evidence to support this prediction with respect to HIPV-mediated priming. The project will test the hypothesis that plants responding to HIPVs will incur measurable fitness costs that will be less severe than costs of induced resistance, and that HIPV-primed plants will produce offspring with altered physiology indicative of priming (i.e., they will be "Primed to be Primed"). This project will address a key gap in our understanding of defense priming. The project includes post-doctoral, graduate and undergraduate training. Undergraduates will be required from a diverse population of historically underrepresented groups at the University of Louisville. Citizen science outreach is included through the "Million Leaf Project" where participants learn to quantify herbivore damage to leaves and develop their own hypotheses related to the ecology and evolution of plant-herbivore interactions.