title: PIPKs are essential for rhizoid elongation and caulonemal cell development in the moss Physcomitrella patens.
abstract: PtdIns-4,5-bisphosphate is a lipid messenger of eukaryotic cells that plays a critical role in processes such as cytoskeleton organization, intracellular vesicular trafficking, secretion, cell motility, regulation of ion channels and nuclear signalling pathways. The enzymes responsible for the synthesis of PtdIns(4,5)P₂ are phosphatidylinositol phosphate kinases (PIPKs). The moss Physcomitrella patens contains two PIPKs, PpPIPK1 and PpPIPK2. To study their physiological role, both genes were disrupted by targeted homologous recombination and as a result mutant plants with lower PtdIns(4,5)P₂ levels were obtained. A strong phenotype for pipk1, but not for pipk2 single knockout lines, was obtained. The pipk1 knockout lines were impaired in rhizoid and caulonemal cell elongation, whereas pipk1-2 double knockout lines showed dramatic defects in protonemal and gametophore morphology manifested by the absence of rapidly elongating caulonemal cells in the protonemal tissue, leafy gametophores with very short rhizoids, and loss of sporophyte production. pipk1 complemented by overexpression of PpPIPK1 fully restored the wild-type phenotype whereas overexpression of the inactive PpPIPK1E885A did not. Overexpression of PpPIPK2 in the pipk1-2 double knockout did not restore the wild-type phenotype demonstrating that PpPIPK1 and PpPIPK2 are not functionally redundant. In vivo imaging of the cytoskeleton network revealed that the shortened caulonemal cells in the pipk1 mutants was the result of the absence of the apicobasal gradient of cortical F-actin cables normally observed in wild-type caulonemal cells. Our data indicate that both PpPIPKs play a crucial role in the development of the moss P. patens, and particularly in the regulation of tip growth.
authors.affiliation: Department of Biochemistry, Centre for Chemistry and Chemical Engineering, Lund University, PO Box 124, SE-22100 Lund, Sweden. llborelli@fc.ul.pt
authors.forename: Laura
authors.initials: L
authors.lastname: Saavedra
authors.forename: Virginia
authors.initials: V
authors.lastname: Balbi
authors.forename: Jennifer
authors.initials: J
authors.lastname: Lerche
authors.forename: Koji
authors.initials: K
authors.lastname: Mikami
authors.forename: Ingo
authors.initials: I
authors.lastname: Heilmann
authors.forename: Marianne
authors.initials: M
authors.lastname: Sommarin
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D000199:Actins / Q000378:metabolism; D019943:Amino Acid Substitution; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D019068:Bryopsida / Q000201:enzymology / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D003571:Cytochalasin B / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant; D059765:Homologous Recombination; D010641:Phenotype; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000032:analysis / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D053778:Thiazolidines / Q000494:pharmacology
chemical_list: D000199:Actins; D019086:Bridged Bicyclo Compounds, Heterocyclic; D019269:Phosphatidylinositol 4,5-Diphosphate; D010940:Plant Proteins; D053778:Thiazolidines; D003571:Cytochalasin B; D017853:Phosphotransferases (Alcohol Group Acceptor); C037068:latrunculin B