Research Training Group 2498

Research Training Group 2498

Communication and Dynamics of Plant Cell Compartments

Projects


Nuclear-cytoplasmic shuttling of plant PI4P 5-kinases

Project Leader// Prof. Dr. Mareike Heilmann

Graduate// Lennart Schwalgun

MLU, Inst. of Biochemistry and Biotechnology
Dept. of Plant Biochemistry
Nuclear Phosphoinositides


Phosphatidylinositol 4-phosphate 5-kinases (PI4P 5-kinases or PIP5Ks) are responsible for the production of the signaling lipid, phosphatidylinositol 4,5- bisphosphate (PI(4,5)P2), which is a minor component of eukaroytic membranes and is present in a variety of subcellular locations, including the plasma membrane and the nucleus. PI(4,5)P2 directly affects a broad range of physiological processes and signaling pathways by acting as a lipid ligand for PI(4,5)P2-dependent effector proteins. The subcellular targeting of PIP5Ks is dynamic and allows the specific and temporary production of PI(4,5)P2 in certain cellular locations to initiate particular local effects. The presence of PIP5Ks and of PI(4,5)P2 in plant nuclei has previously been reported. In all eukaryotic systems the understanding of events regulated by phosphoinositides in the cytosol and at the plasma membrane is far deeper than that of nuclear phosphoinositides. PI(4,5)P2-dependent regulation of nuclear processes may be important for plant function, as it has been reported for other eukaryotes. In the Arabidopsis genome PIP5Ks are encoded as a family of 11 isoforms (PIP5K1-PIP5K11). A bioinformatics analysis of the deduced amino acid sequences indicates the presence of at least one recognizable NLS in each of the eleven PIP5K isoforms. Nuclear localization of plant PIP5Ks appears dynamic and is not observed at all times or in cells of all plant tissues. Therefore, we aim to conduct a systematic analysis of when and where nuclear localization of PIP5Ks occurs in plants. It is the working hypothesis of this project that nuclear-cytoplasmic shuttling of PIP5Ks depends on cellular requirements which might change between developmental stages or tissues, or upon stress conditions. We furthermore hypothesize that nuclear localization of PIP5Ks is regulated by NLS that might be masked or active, depending on posttranslational modifications of PIP5Ks, and we have already identified a potential phosphorylation site within the functional NLS of PIP5K2; however, the effect of this modification is unclear. Research in this project is subdivided in the following work packages:

  1. Systematic analysis of conditions for nuclear localization of selected PIP5Ks in plant cells
  2. Functional characterization of further predicted NLS in Arabidopsis PIP5K isoforms
  3. Generation of nucleus-excluded PIP5K variants with dysfunctional NLS
  4. Mutant complementation tests with PIP5Ks carrying dysfunctional NLS
  5. Identification of post-translational modifications of PIP5Ks that influence NLS function
  6. Functional analysis of PTMs with effects on NLS activity