Inositol Synthesis and Catabolism in Plants

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This project utilizes molecular, genetic and biochemical tools to address a fundamental pathway present in most organisms that gives rise to a large number of required metabolites. Myo-inositol synthesis and catabolism is crucial in many multiceullar eukaryotes for production of phosphatidylinositol signaling molecules, glycerophosphoinositide membrane anchors, cell wall pectic non-cellulosic polysaccharides, Vitamin C, and several other molecules. Myo-inositol synthesis and catabolism are especially important in plants and ground-breaking biochemical experiments from the 1960's and 70's defined all of the major enzymes involved. Multigene families encoding myo-inositol monophosphatase (IMP; EC 3.1.3.25), and myo-inositol oxygenase (MIOX; E.C. 1.13.99.1) enzymes are present in the plant model system, Arabidopsis thaliana. The project will address the hypothesis that the IMP and MIOX genes have specialized roles in providing inositol for various pathways. To test this hypothesis, IMP and MIOX expression patterns will be examined. To address whether the different IMP and MIOX isoforms have different catalytic activities, recombinant proteins will be produced and their substrate specificities determined. Complementing this approach will be a genetic analysis which is crucial for determining function in vivo. Metabolic profiling by gas chromatography-mass spectrometry will be utilized to determine the effect of each isoform on levels of the myo-inositol, phosphatidylinositol, D-glucuronic acid, galactinol, ascorbic acid, and other inositol metabolites as required. The inositol synthesis and catabolism pathway provides inositol for many required cellular functions of both plants and animals. This project will investigate how a model plant controls the synthesis of inositol to meet its varying needs. Since the dynamics of inositol turnover in plants can impact the environment through phosphorous contamination of soil, this research will provide knowledge about possible ways to limit such contamination. As well, inositol synthesis is altered in diseases such as diabetes, Down's syndrome, Alzheimer's and bipolar disorder. Thus investigating the basic science of inositol metabolism is vital also for understanding the pathology of these diseases.