Mutant Name: cobra

Gene Name COB
Protein Name glycosylphosphatidylinositol-anchored protein
Mutagen EMS
Category forward genetics
Organism Arabidopsis thaliana
Ecotype Col
Donor
General Description 1.cobra mutants have abnormal roots that expand radially rather than longitudinally under certain growth conditions.
2.loss of anisotropic expansion in cob mutants is accompanied by disorganization of the orientation of cellulose microfibrils and subsequent reduction of crystalline cellulose.
3.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.
Organ Specificity COB was shown to be expressed in most plant organs on the basis of RNA gel blots and RT-PCR analyses. Assaying GUS activity at different times in the plant life cycle revealed that COB was expressed only postembryonically, with its strongest expression in the root.
Impact on Wall 1.Root cells in cob appear to be expanded more in a radial than in a longitudinal orientation while maintaining cell volume.
2.loss of anisotropic expansion in cob mutants is accompanied by disorganization of the orientation of cellulose microfibrils and subsequent reduction of crystalline cellulose.
Impact on Sugar Composition Measurements showed that there was a highly significant difference (P < 0.003) between wild-type roots, which had a mean value of 133± 28 µg cellulose (mg cell wall)1, and cob roots which had a mean value of 89 ± 2µg cellulose (mg/cell wall).
Reference 1.Roudier F, Fernandez AG, Fujita M, Himmelspach R, Borner GH, Schindelman G, Song S, Baskin TI, Dupree P, Wasteneys GO, Benfey PN. COBRA, an Arabidopsis Extracellular Glycosylphosphatidylinositol-Anchored Protein, Specifically Controls Highly Anisotropic Expansion through Its Involvement in Cellulose Microfibril Orientation. Plant Cell. 2005 Apr 22

2. Roudier F, Schindelman G, DeSalle R, Benfey PN. The COBRA family of putative GPI-anchored proteins in Arabidopsis. A new fellowship in expansion. Plant Physiol. 2002 Oct;130(2):538-48.

3. Schindelman G, Morikami A, Jung J, Baskin TI, Carpita NC, Derbyshire P, McCann MC, Benfey PN. COBRA encodes a putative GPI-anchored protein, which is polarly localized and necessary for oriented cell expansion in Arabidopsis. Genes Dev. 2001 May 1;15(9):1115-27.