9409089 Mehdy Little is known concerning the molecular mechanisms regulating mRNA stability in plants although direct and indirect evidence indicates that it is an important determinant in the expression of many genes. The plant defense response is characterized by a rapid loss of mRNAs encoding the bean proline-rich protein, PvPRP1, an extensin, Beta-tubulin as well as a number of unknown proteins. Among these mRNAs, the PvPRP1 mRNA down-regulation is currently the best characterized mechanistically. The PvPRP1 mRNA is destabilized after elicitor treatment and a protein which specifically binds this transcript has been identified (PRP-BP). Purification of the RNA binding protein will be a major goal in order to define its biochemical properties including apparent post- translational activation by elicitor treatment and interaction with the PvPRP1 mRNA. In addition, availability of the purified protein will allow cloning of its encoding gene and production of PRP-BP- specific antibodies for immunocytochemical localization of the protein. One of the most rapid processes triggered by exposure to pathogens is the striking release of active oxygen species (AOS) which is termed the oxidative burst. The possibility that AOS serve as signal intermediates which induce phytoalexin biosynthesis has received considerable attention. However, the mechanism(s) of AOS regulation of phytoalexin accumulation and other intracellular defense-related changes is unknown. This research will use biochemical and molecular approaches to clarify the roles of AOS and changes in cellular glutathione levels in elicitor-induced signalling pathways leading to regulation of PvPRP1 and phytoalexin pathway mRNA levels. The experimental system being studied is the interaction between the fungal pathogen and the host plant (bean). At a more general level, the results of these studies will contribute to our understanding of oxidative stress regulation of gene expression. ***
