KOBITO1 encodes a novel plasma membrane protein necessary for normal synthesis of cellulose during cell expansion in Arabidopsis.
The cell wall is the major limiting factor for plant growth. Wall extension is thought to result from the loosening of its structure. However, it is not known how this is coordinated with wall synthesis. We have identified two novel allelic cellulose-deficient dwarf mutants, kobito1-1 and kobito1-2 (kob1-1 and kob1-2). The cellulose deficiency was confirmed by the direct observation of microfibrils in most recent wall layers of elongating root cells. In contrast to the wild type, which showed transversely oriented parallel microfibrils, kob1 microfibrils were randomized and occluded by a layer of pectic material. No such changes were observed in another dwarf mutant, pom1, suggesting that the cellulose defect in kob1 is not an indirect result of the reduced cell elongation. Interestingly, in the meristematic zone of kob1 roots, microfibrils appeared unaltered compared with the wild type, suggesting a role for KOB1 preferentially in rapidly elongating cells. KOB1 was cloned and encodes a novel, highly conserved, plant-specific protein that is plasma membrane bound, as shown with a green fluorescent protein-KOB1 fusion protein. KOB1 mRNA was present in all organs investigated, and its overexpression did not cause visible phenotypic changes. KOB1 may be part of the cellulose synthesis machinery in elongating cells, or it may play a role in the coordination between cell elongation and cellulose synthesis.
Pagant
Silvère
S
Laboratoire de Biologie Cellulaire, Institut National de la Recherche Agronomique, Route de Saint-Cyr, 78026 Versailles Cedex, France.
Bichet
Adeline
A
Sugimoto
Keiko
K
Lerouxel
Olivier
O
Desprez
Thierry
T
McCann
Maureen
M
Lerouge
Patrice
P
Vernhettes
Samantha
S
Höfte
Herman
H
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D002473:Cell Wall / Q000502:physiology*; D002482:Cellulose / Q000096:biosynthesis*; D005936:Glucans / Q000378:metabolism; D005964:Glucosyltransferases / Q000378:metabolism; D049452:Green Fluorescent Proteins; D018546:Hypocotyl / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D008031:Lignin / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D020894:Microfibrils / Q000378:metabolism / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
D029681:Arabidopsis Proteins; D002482:Cellulose; D005936:Glucans; D005964:Glucosyltransferases; D049452:Green Fluorescent Proteins; D008031:Lignin; D008164:Luminescent Proteins; D008565:Membrane Proteins; C469256:KOB1 protein, Arabidopsis; C048306:callose; C063760:cellulose synthase (GDP-forming)