Date of Award

1-1-2009

Document Type

Campus Access Dissertation

Department

Biological Sciences

First Advisor

Johannes W. Stratmann

Abstract

Plants must defend themselves from a wide array of biotic stresses, including herbivorous insects, phytopathogenic fungi, bacteria, and viruses. The varied nature of these stressors requires that the plant recognize a specific stress and mount an appropriate defense response. The defense response in plants involves initiating multi-component signal transduction processes that lead to the activation of defense response genes. In tomato, feeding by herbivorous insects initiates the systemin-mediated wound signaling pathway. Systemin is an 18 amino acid peptide that binds to the systemin receptor and initiates an intracellular signaling pathway that results in the accumulation of defense compounds in the leaves of the plant. The systemin signaling pathway involves the activation of a MAP Kinase cascade. This dissertation details the characterization of components of the systemin-responsive MAPK cascade, including MAPKs, the putative systemin receptor, and MAPK Kinases. One of the initial signaling events after systemin perception involves ion fluxes that result in extracellular alkalinization; however, changes in the extracellular pH are neither sufficient nor required for activation of MAPKs in the systemin signaling pathway. Two MAPK Kinases, MKK2 and MKK4 are thought to be involved in the systemin signaling pathway, upstream of well-characterized MAPKs, MPK1/2 and MPK3. Through the use of a protoplast transient expression assay, I have confirmed that MKK2 can phosphorylate MPK1/2 and MPK3, but MKK4 is not expressed in protoplasts. I have shown that negative regulation of MKK4 via conventional protein degradation mechanisms is not responsible for the lack of expression in the protoplast system.

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