title: The Arabidopsis sku6/spiral1 gene encodes a plus end-localized microtubule-interacting protein involved in directional cell expansion.
abstract: The sku6-1 mutant of Arabidopsis thaliana exhibits altered patterns of root and organ growth. sku6 roots, etiolated hypocotyls, and leaf petioles exhibit right-handed axial twisting, and root growth on inclined agar media is strongly right skewed. The touch-dependent sku6 root skewing phenotype is suppressed by the antimicrotubule drugs propyzamide and oryzalin, and right skewing is exacerbated by cold treatment. Cloning revealed that sku6-1 is allelic to spiral1-1 (spr1-1). However, modifiers in the Columbia (Col) and Landsberg erecta (Ler) ecotype backgrounds mask noncomplementation in sku6-1 (Col)/spr1-1 (Ler) F1 plants. The SPR1 gene encodes a plant-specific 12-kD protein that is ubiquitously expressed and belongs to a six-member gene family in Arabidopsis. An SPR1:green fluorescent protein (GFP) fusion expressed in transgenic seedlings localized to microtubules within the cortical array, preprophase band, phragmoplast, and mitotic spindle. SPR1:GFP was concentrated at the growing ends of cortical microtubules and was dependent on polymer growth state; the microtubule-related fluorescence dissipated upon polymer shortening. The protein has a repeated motif at both ends, separated by a predicted rod-like domain, suggesting that it may act as an intermolecular linker. These observations suggest that SPR1 is involved in microtubule polymerization dynamics and/or guidance, which in turn influences touch-induced directional cell expansion and axial twisting.
authors.affiliation: Department of Biological Sciences, Illinois State University, Normal, Illinois 61790, USA. jcsedbr@ilstu.edu
authors.forename: John C
authors.initials: JC
authors.lastname: Sedbrook
authors.forename: David W
authors.initials: DW
authors.lastname: Ehrhardt
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Fisher
authors.forename: Wolf-Rüdiger
authors.initials: WR
authors.lastname: Scheible
authors.forename: Chris R
authors.initials: CR
authors.lastname: Somerville
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology* / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001549:Benzamides / Q000494:pharmacology; D048429:Cell Size; D003001:Cloning, Molecular; D004136:Dinitrobenzenes / Q000494:pharmacology; D017343:Genes, Plant / Q000235:genetics; D008868:Microtubule Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development; D030821:Plants, Genetically Modified; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012399:Rotation; D036226:Seedlings / Q000235:genetics / Q000254:growth & development; D013424:Sulfanilamides
chemical_list: D029681:Arabidopsis Proteins; D001549:Benzamides; D004136:Dinitrobenzenes; D008868:Microtubule Proteins; D008869:Microtubule-Associated Proteins; D012333:RNA, Messenger; C487570:SPR1 protein, Arabidopsis; D013424:Sulfanilamides; C001059:pronamide; C012465:oryzalin