title: Inactivation of plasma membrane-localized CDPK-RELATED KINASE5 decelerates PIN2 exocytosis and root gravitropic response in Arabidopsis.
abstract: CRK5 is a member of the Arabidopsis thaliana Ca(2+)/calmodulin-dependent kinase-related kinase family. Here, we show that inactivation of CRK5 inhibits primary root elongation and delays gravitropic bending of shoots and roots. Reduced activity of the auxin-induced DR5-green fluorescent protein reporter suggests that auxin is depleted from crk5 root tips. However, no tip collapse is observed and the transcription of genes for auxin biosynthesis, AUXIN TRANSPORTER/AUXIN TRANSPORTER-LIKE PROTEIN (AUX/LAX) auxin influx, and PIN-FORMED (PIN) efflux carriers is unaffected by the crk5 mutation. Whereas AUX1, PIN1, PIN3, PIN4, and PIN7 display normal localization, PIN2 is depleted from apical membranes of epidermal cells and shows basal to apical relocalization in the cortex of the crk5 root transition zone. This, together with an increase in the number of crk5 lateral root primordia, suggests facilitated auxin efflux through the cortex toward the elongation zone. CRK5 is a plasma membrane-associated kinase that forms U-shaped patterns facing outer lateral walls of epidermis and cortex cells. Brefeldin inhibition of exocytosis stimulates CRK5 internalization into brefeldin bodies. CRK5 phosphorylates the hydrophilic loop of PIN2 in vitro, and PIN2 shows accelerated accumulation in brefeldin bodies in the crk5 mutant. Delayed gravitropic response of the crk5 mutant thus likely reflects defective phosphorylation of PIN2 and deceleration of its brefeldin-sensitive membrane recycling.
authors.affiliation: Institute of Plant Biology, Biological Research Center, H-6726 Szeged, Hungary.
authors.forename: Gábor
authors.initials: G
authors.lastname: Rigó
authors.forename: Ferhan
authors.initials: F
authors.lastname: Ayaydin
authors.forename: Olaf
authors.initials: O
authors.lastname: Tietz
authors.forename: Laura
authors.initials: L
authors.lastname: Zsigmond
authors.forename: Hajnalka
authors.initials: H
authors.lastname: Kovács
authors.forename: Anikó
authors.initials: A
authors.lastname: Páy
authors.forename: Klaus
authors.initials: K
authors.lastname: Salchert
authors.forename: Zsuzsanna
authors.initials: Z
authors.lastname: Darula
authors.forename: Katalin F
authors.initials: KF
authors.lastname: Medzihradszky
authors.forename: László
authors.initials: L
authors.lastname: Szabados
authors.forename: Klaus
authors.initials: K
authors.lastname: Palme
authors.forename: Csaba
authors.initials: C
authors.lastname: Koncz
authors.forename: Agnes
authors.initials: A
authors.lastname: Cséplo
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D005089:Exocytosis; D018506:Gene Expression Regulation, Plant; D018522:Gravitropism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D009154:Mutation; D010766:Phosphorylation; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D030821:Plants, Genetically Modified; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
chemical_list: D029681:Arabidopsis Proteins; D049452:Green Fluorescent Proteins; D007210:Indoleacetic Acids; D017346:Protein Serine-Threonine Kinases; D011956:Receptors, Cell Surface; C117013:AT5G57090 protein, Arabidopsis; C420215:CRK5 protein, Arabidopsis