title: Characterization of the Arabidopsis augmin complex uncovers its critical function in the assembly of the acentrosomal spindle and phragmoplast microtubule arrays.
abstract: Plant cells assemble the bipolar spindle and phragmoplast microtubule (MT) arrays in the absence of the centrosome structure. Our recent findings in Arabidopsis thaliana indicated that AUGMIN subunit3 (AUG3), a homolog of animal dim γ-tubulin 3, plays a critical role in γ-tubulin-dependent MT nucleation and amplification during mitosis. Here, we report the isolation of the entire plant augmin complex that contains eight subunits. Among them, AUG1 to AUG6 share low sequence similarity with their animal counterparts, but AUG7 and AUG8 share homology only with proteins of plant origin. Genetic analyses indicate that the AUG1, AUG2, AUG4, and AUG5 genes are essential, as stable mutations in these genes could only be transmitted to heterozygous plants. The sterile aug7-1 homozygous mutant in which AUG7 expression is significantly reduced exhibited pleiotropic phenotypes of seriously retarded vegetative and reproductive growth. The aug7-1 mutation caused delocalization of γ-tubulin in the mitotic spindle and phragmoplast. Consequently, spindles were abnormally elongated, and their poles failed to converge, as MTs were splayed to discrete positions rendering deformed arrays. In addition, the mutant phragmoplasts often had disorganized MT bundles with uneven edges. We conclude that assembly of MT arrays during plant mitosis depends on the augmin complex, which includes two plant-specific subunits.
authors.affiliation: Department of Plant Biology, University of California, Davis, California 95616, USA.
authors.forename: Takashi
authors.initials: T
authors.lastname: Hotta
authors.forename: Zhaosheng
authors.initials: Z
authors.lastname: Kong
authors.forename: Chin-Min Kimmy
authors.initials: CM
authors.lastname: Ho
authors.forename: Cui Jing Tracy
authors.initials: CJ
authors.lastname: Zeng
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Horio
authors.forename: Sophia
authors.initials: S
authors.lastname: Fong
authors.forename: Trang
authors.initials: T
authors.lastname: Vuong
authors.forename: Yuh-Ru Julie
authors.initials: YR
authors.lastname: Lee
authors.forename: Bo
authors.initials: B
authors.lastname: Liu
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D018385:Centrosome / Q000378:metabolism*; D056130:Gametogenesis, Plant / Q000235:genetics; D017343:Genes, Plant / Q000235:genetics; D055993:Germ Cells, Plant / Q000166:cytology / Q000254:growth & development; D018519:Meristem / Q000166:cytology / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism*; D008938:Mitosis; D009024:Morphogenesis; D046912:Multiprotein Complexes / Q000302:isolation & purification / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D011485:Protein Binding; D021122:Protein Subunits / Q000302:isolation & purification / Q000378:metabolism; D021381:Protein Transport; D013045:Species Specificity; D008941:Spindle Apparatus / Q000378:metabolism*; D014404:Tubulin / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D046912:Multiprotein Complexes; D021122:Protein Subunits; D014404:Tubulin