title: COBRA, an Arabidopsis extracellular glycosyl-phosphatidyl inositol-anchored protein, specifically controls highly anisotropic expansion through its involvement in cellulose microfibril orientation.
abstract: The orientation of cell expansion is a process at the heart of plant morphogenesis. Cellulose microfibrils are the primary anisotropic material in the cell wall and thus are likely to be the main determinant of the orientation of cell expansion. COBRA (COB) has been identified previously as a potential regulator of cellulose biogenesis. In this study, characterization of a null allele, cob-4, establishes the key role of COB in controlling anisotropic expansion in most developing organs. Quantitative polarized-light and field-emission scanning electron microscopy reveal that loss of anisotropic expansion in cob mutants is accompanied by disorganization of the orientation of cellulose microfibrils and subsequent reduction of crystalline cellulose. Analyses of the conditional cob-1 allele suggested that COB is primarily implicated in microfibril deposition during rapid elongation. Immunodetection analysis in elongating root cells revealed that, in agreement with its substitution by a glycosylphosphatidylinositol anchor, COB was polarly targeted to both the plasma membrane and the longitudinal cell walls and was distributed in a banding pattern perpendicular to the longitudinal axis via a microtubule-dependent mechanism. Our observations suggest that COB, through its involvement in cellulose microfibril orientation, is an essential factor in highly anisotropic expansion during plant morphogenesis.
authors.affiliation: Department of Biology, Duke University, Durham, North Carolina 27708, USA.
authors.forename: François
authors.initials: F
authors.lastname: Roudier
authors.forename: Anita G
authors.initials: AG
authors.lastname: Fernandez
authors.forename: Miki
authors.initials: M
authors.lastname: Fujita
authors.forename: Regina
authors.initials: R
authors.lastname: Himmelspach
authors.forename: Georg H H
authors.initials: GH
authors.lastname: Borner
authors.forename: Gary
authors.initials: G
authors.lastname: Schindelman
authors.forename: Shuang
authors.initials: S
authors.lastname: Song
authors.forename: Tobias I
authors.initials: TI
authors.lastname: Baskin
authors.forename: Paul
authors.initials: P
authors.lastname: Dupree
authors.forename: Geoffrey O
authors.initials: GO
authors.lastname: Wasteneys
authors.forename: Philip N
authors.initials: PN
authors.lastname: Benfey
mesh_terms: D017360:Arabidopsis / Q000254:growth & development* / Q000378:metabolism* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology; D049108:Cell Enlargement; D002462:Cell Membrane / Q000378:metabolism; D016764:Cell Polarity / Q000502:physiology; D002473:Cell Wall / Q000378:metabolism* / Q000648:ultrastructure; D002482:Cellulose / Q000378:metabolism*; D017261:Glycosylphosphatidylinositols / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D020894:Microfibrils / Q000378:metabolism* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D009154:Mutation / Q000235:genetics; D021381:Protein Transport / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; C427475:COB protein, Arabidopsis; D017261:Glycosylphosphatidylinositols; D008562:Membrane Glycoproteins; D002482:Cellulose