title: Rice Brittle culm 6 encodes a dominant-negative form of CesA protein that perturbs cellulose synthesis in secondary cell walls.
abstract: The brittle culm (bc) mutants of Gramineae plants having brittle skeletal structures are valuable materials for studying secondary cell walls. In contrast to other recessive bc mutants, rice Bc6 is a semi-dominant bc mutant with easily breakable plant bodies. In this study, the Bc6 gene was cloned by positional cloning. Bc6 encodes a cellulose synthase catalytic subunit, OsCesA9, and has a missense mutation in its highly conserved region. In culms of the Bc6 mutant, the proportion of cellulose was reduced by 38%, while that of hemicellulose was increased by 34%. Introduction of the semi-dominant Bc6 mutant gene into wild-type rice significantly reduced the percentage of cellulose, causing brittle phenotypes. Transmission electron microscopy analysis revealed that Bc6 mutation reduced the cell wall thickness of sclerenchymal cells in culms. In rice expressing a reporter construct, BC6 promoter activity was detected in the culms, nodes, and flowers, and was localized primarily in xylem tissues. This expression pattern was highly similar to that of BC1, which encodes a COBRA-like protein involved in cellulose synthesis in secondary cell walls in rice. These results indicate that BC6 is a secondary cell wall-specific CesA that plays an important role in proper deposition of cellulose in the secondary cell walls.
authors.affiliation: Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan.
authors.forename: Toshihisa
authors.initials: T
authors.lastname: Kotake
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Aohara
authors.forename: Ko
authors.initials: K
authors.lastname: Hirano
authors.forename: Ami
authors.initials: A
authors.lastname: Sato
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Kaneko
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Tsumuraya
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Takatsuji
authors.forename: Shinji
authors.initials: S
authors.lastname: Kawasaki
mesh_terms: D000595:Amino Acid Sequence; D002473:Cell Wall / Q000378:metabolism*; D002482:Cellulose / Q000096:biosynthesis*; D003001:Cloning, Molecular; D005964:Glucosyltransferases / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D012275:Oryza / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000648:ultrastructure
chemical_list: D002482:Cellulose; D005964:Glucosyltransferases; C478648:cellulose synthase