Rebekka Wild1,*, Ruta Gerasimaite2,*, Ji-Yul Jung3,*, Vincent Truffault4, Igor Pavlovic5, Andrea Schmidt2, Adolfo Saiardi6, Henning Jacob Jessen5,7, Yves Poirier3,†, Michael Hothorn1,†, Andreas Mayer2,†
1Structural Plant Biology Laboratory, Department of Botany and Plant Biology, University of Geneva, Switzerland.
2Department of Biochemistry, University of Lausanne, Switzerland.
3Department of Plant Molecular Biology, University of Lausanne, Switzerland.
4Department of Biochemistry, Max Planck Institute for Developmental Biology, Tubingen, Germany.
5Department of Chemistry and Pharmacy, University of Zurich, Switzerland.
6Medical Research Council Laboratory for Molecular Cell Biology, University College London, UK.
7Institute of Organic Chemistry, Albert-Ludwigs-University Freiburg, Germany.
†Corresponding author : Yves Poirier; Michael Hothorn; Andreas Mayer
* These authors contributed equally to this work.
Phosphorus is a macronutrient taken up by cells as inorganic phosphate (Pi). How cells sense cellular Pi levels is poorly characterized. Here we report that SPX domains, which are found in eukaryotic phosphate transporters, signaling proteins and inorganic polyphosphate polymerases, provide a basic binding surface for inositol polyphosphate signaling molecules (InsPs), whose concentrations change in response to Pi availability. Substitutions of critical binding surface residues impair InsP binding in vitro, inorganic polyphosphate synthesis in yeast and Pi transport in Arabidopsis. In plants, InsPs trigger the association of SPX proteins with transcription factors to regulate Pi starvation responses. We propose that InsPs communicate cytosolic Pi levels to SPX domains and enable them to interact with a multitude of proteins to regulate Pi uptake, transport and storage in fungi, plants and animals.