title: Phosphorylation and activation of PINOID by the phospholipid signaling kinase 3-phosphoinositide-dependent protein kinase 1 (PDK1) in Arabidopsis.
abstract: Activity of the serine-threonine protein kinase PINOID (PID) has been implicated in the asymmetrical localization of the membrane-associated PINFORMED (PIN) family of auxin transport facilitators. However, the means by which PID regulates PIN protein distribution is unknown. We have used recombinant PID protein to dissect the regulation of PID activity in vitro. We demonstrate that intramolecular PID autophosphorylation is required for the ability of PID to phosphorylate an exogenous substrate. PID-like mammalian AGC kinases act in a phosphorylation cascade initiated by the phospholipid-associated kinase, 3-phosphoinositide-dependent protein kinase 1 (PDK1), which binds to the C-terminal hydrophobic PDK1-interacting fragment (PIF) domain found in PDK1 substrates. We find that Arabidopsis PDK1 interacts with PID, and that transphosphorylation by PDK1 increases PID autophosphorylation. We show that a PID activation loop serine is required for PDK1-dependent PID phosphorylation. This activation is rapid and requires the PIF domain. Cell extracts from flowers and seedling shoots dramatically increase PID phosphorylation in a tissue-specific manner. A PID protein variant in which the PIF domain was mutated failed to be activated by the seedling shoot extracts. PID immunoprecipitated from Arabidopsis cells in which PDK1 expression was inhibited by RNAi showed a dramatic reduction in transphosphorylation of myelin basic protein substrate. These results indicate that AtPDK1 is a potent enhancer of PID activity and provide evidence that phospholipid signaling may play a role in the signaling processes controlling polar auxin transport.
authors.affiliation: Department of Molecular, Cell, and Developmental Biology and Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA.
authors.forename: Hicham
authors.initials: H
authors.lastname: Zegzouti
authors.forename: Richard G
authors.initials: RG
authors.lastname: Anthony
authors.forename: Nadine
authors.initials: N
authors.lastname: Jahchan
authors.forename: László
authors.initials: L
authors.lastname: Bögre
authors.forename: Sioux K
authors.initials: SK
authors.lastname: Christensen
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002457:Cell Extracts / Q000494:pharmacology; D004789:Enzyme Activation; D047468:Immunoprecipitation; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000235:genetics; D015398:Signal Transduction; D015533:Transcriptional Activation
chemical_list: D029681:Arabidopsis Proteins; D002457:Cell Extracts; C405165:PINOID protein, Arabidopsis; D064413:3-Phosphoinositide-Dependent Protein Kinases; D017346:Protein Serine-Threonine Kinases; D002118:Calcium