mesc3399

Dr. Meredith Schuman

   
   Department of Molecular Ecology
 Phone:+49 (0)3641 57 1116Max Planck Institute for Chemical Ecology
 Fax:+49 (0)3641 57 1102Hans-Knöll-Straße 8
  emailD-07745 Jena

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PhD Thesis

2012
The response of Nicotiana attenuata plants to herbivory: polymorphism and functions in nature
Friedrich-Schiller-Universität Jena, Biologisch-Pharmazeutische Fakultät
First Supervisor: Prof. I.T. Baldwin
Co-Supervisor(s): Dr. M. Schöttner, Prof. Dr. J. Gershenzon

Abstract
Chemical ecology began with the study of plant-insect interactions. In the nineteenth century, biologists began to realize the profound importance of plant chemistry in determining herbivore choice. Given that plants are the primary source of food in terrestrial ecosystems, the role of plant metabolites in herbivore choice and performance translates to a role in structuring ecological communities. This work describes natural variation in volatile and non-volatile herbivore-induced metabolites in the native tobacco /Nicotiana attenuata/, and experiments to test the defensive functions of some of these metabolites in nature. The variation described includes natural variation among accessions in herbivore-induced signaling cascades and metabolite production, as well as complex metabolic variation in a class of terpenoid specialized metabolites, the 17-hydroxygeranyllinalool diterpene glycosides (HGL-DTGs), in response to herbivore-induced signaling. I dissect the contribution of herbivore-induced jasmonate signaling to the regulation of different traits, and present evidence from wild plants that jasmonate regulation is a suitable, although not exclusive criterion for identifying candidate anti-herbivore defense metabolites. I furthermore present evidence that some of these metabolites do in fact function as anti-herbivore defenses for /N. attenuata/ plants in their natural habitat. Specifically, I demonstrate that HGL-DTGs effectively reduce damage from native specialist herbivores, and that green leaf volatile emission mediates indirect defense and increases plant reproduction in nature. The determination of metabolite functions under controlled laboratory conditions is essential but can be misleading: although trypsin protease inhibitors (TPIs) have become a classic example of anti-herbivore defense, I show that they provide little or no direct benefit to plants in the field, and may instead function to support indirect defense. A combination of laboratory and field assays using both native accessions, and isogenic lines genetically modified in single traits of interest, permits the discovery of plant defense strategies, the elucidation of complex regulatory networks, and the demonstration of their importance.