The Pathway Through Inositol is the Pathway to Stress Tolerance

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9507375 Bohnert This research focuses on the genes and proteins in plants catalyzing an essential pathway in all organisms, the biosynthesis of myo-inositol, MI. The enzyme MI-IP synthase converts glucose 6-phosphate to myo-inositol 1-phosphate and a phosphatase produces MI. The two products of the pathway play a central and essential role in providing signalling molecules, in membrane biogenesis and - in plants - phosphate storage, the production of oligosaccharides, vegetative carbohydrate storage, and the production of gums and mucilages. An extension of the pathway beyond MI is the inositol methylation pathway which produces a number of mono- or di- methylated inositols. The methylated inositols may have a function in osmotic adjustment with the methyl groups provided follwing an increase in photorespiration under stress conditions. Methylated inositols are found in species that tolerate high salinity or drought conditions. Families with predominantly or exclusively glycophytic species that are not drought tolerant seem to lack gense that lead to an extension from MI to, for example, D- pinitol. To address this point, Drs. Bohnert and Jensen propose a comparative molecular, biochemical and physiological analysis of MI biosynthesis and the extension of the pathway to D-pinitol. First, the biochemical characteristics of the pathway enzymes, flux and flux control for carbon partitioning from glucose 6-phosphate will be anlyzed in the glycophyte, rice, and in a halophyte, ice plant. MI biosynthesis is localized to the cytosol and chlorophlasts. Thus, one analysis will be to gauge the control of relative fluxes through either pathway, and, also, on the stability or sensitivity of MI biosynthesis to external factors in each pathway under stress conditions. Additionally, there are questions about the genetics and genes of the pathway. What is the genetic makeup of the pathway? How many - different - gense are there for the enzymes in each pathway, and how is the pathway controlled during development and in which tissues and cells? Is there a difference in control distinguishing the glycophyte and the halophyte during stress-free growth and under stress?