Regulation of Phosphatidylinositol Phosphate Kinases: Plant-Specific PIPmodulins

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Phosphatidylinositol phosphate 5-kinases (PIPKs) are the enzymes that synthesize PtdIns(4,5)P2, an important signaling lipid found in plants and animals. Recent comparative biochemical characterizations make a compelling argument that plant PIPKs are unique, multifunctional proteins which define plant phosphoinositide (PI) signaling. In contrast to mammalian PIPKs, Arabidopsis PIPK1 (AtPIPK1) binds directly to actin without needing adaptor proteins. Furthermore, AtPIPK1 has an extended N-terminal domain that binds negatively charged lipids including PtdIns(4,5)P2. The ability to both synthesize and sequester PtdIns(4,5)P2 makes this the ultimate PIPmodulin, a protein predicted to sequester and modulate the impact of PtdIns(4,5)P2 on cellular physiology. No other organism (including mammals, yeast, C. elegans and Drosophila) has PIPKs that contain similar N-terminal motifs or that bind directly to actin. The hypothesis to be tested is that the plant-specific PIPKs connect membrane lipids to fine actin filaments and that hyperosmotic stress affects both this connection and the activity of the PIPKs. This work will reveal new insights into the mechanisms through which these plant-specific enzymes connect the actin cytoskeleton to membranes and generate PtdIns(4,5)P2-enriched microdomains.The research will have a major impact on the understanding of the fundamental differences in PI metabolism in plants and animals. The research also will impact the careers of one postdoc, one graduate student and at least 3 undergraduates a semester who will work with the group. The undergraduates will be given independent research projects to generate and characterize the recombinant proteins and will help with transforming protoplasts. The undergraduates will write research proposals for the annual University-wide competition and will give a poster presentation on their research at the undergraduate research symposium. Undergraduates in the PIs program routinely win awards for their presentations. Moreover several young scientists from the program have entered into careers in plant biology.