To compensate for the sessile nature of plants, thousands of years of evolution have led to the development of many sophisticated signaling pathways that help plants sense and respond appropriately to different environmental cues. One such signaling pathway is called inositol phosphate signaling. This research dissertation focuses on the inositol phosphate signaling pathway in plants, with emphasis on elucidating how a new class of signaling molecules collectively referred to inositol pyrophosphates are synthesized. Inositol pyrophosphates are an emerging class of "high-energy" intracellular signaling molecules containing one or two diphosphate groups attached to an inositol ring, with suggested roles in bioenergetic homeostasis and inorganic phosphate sensing. Information regarding the biosynthesis of this unique class of signaling molecules in plants is scarce, however the enzymes responsible for their biosynthesis in other eukaryotes have been well described. This work aims to characterize the biochemical activity of the kinase domain (KD) of the Arabidopsis plant diphosphoinositol pentakisphosphate kinase enzymes (AtVIP1 and AtVIP2), and elucidate the biosynthesis pathway of inositol pyrophosphates in plants. Our data indicate that AtVIP1-KD and AtVIP2-KD function primarily as diphosphoinositol pentakisphosphate 5 kinases that phosphorylate this substrate at the 1-position. We also discovered a previously unreported inositol hexakisphosphate kinase activity for the Arabidopsis inositol(1,3,4) triphosphate 5/6kinase enzymes, that can convert InsP6 to InsP7. Together, these enzymes can function in plants to produce inositol pyrophosphates, which have been implicated in signal transduction and phosphate sensing pathways. The significance and potential application of these findings in terms of reduced phytate content and phosphate pollution, improved plant fitness, and improved nutrient use efficiency are discussed. The future outlook of inositol phosphate signaling research is also discussed. / Doctor of Philosophy / Inositol Pyrophosphate Biosynthesis and Subcellular Distribution of Enzymes. Notably, InsP6 which represents the major precursor of PP-InsPs in plants is synthesized in the cytosol, however, it can also be transported into the vacuole by the ABC transporter MRP5. Subcellular localization of enzymes involved in PP-InsP biosynthesis including AtITPK and the kinase domains of AtVIP suggests that these molecules are present in the cytosol and nucleus, and to a smaller extent in the ER. Not shown are the full length and phosphatase domain of AtVIP, which are absent from the nucleus.
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| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/93407 |
| Date | 05 September 2019 |
| Creators | Adepoju, Olusegun Adeboye |
| Contributors | Biochemistry, Gillaspy, Glenda E., McDowell, John M., Tu, Zhijian Jake, Sobrado, Pablo |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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