Characterization of the Arabidopsis Augmin Complex Uncovers Its Critical Function in the Assembly of the Acentrosomal Spindle and Phragmoplast Microtubule Arrays
Characterization of the Arabidopsis Augmin Complex Uncovers Its Critical Function in the Assembly of the Acentrosomal Spindle and Phragmoplast Microtubule Arrays
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DOI：
10.1105/tpc.112.096610
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发表时间：
2012-04-01
期刊：
影响因子：
11.6
通讯作者：
Liu, Bo
中科院分区：
文献类型：
--
作者：
Hotta, Takashi;Kong, Zhaosheng;Liu, Bo
植物细胞在缺乏中心体结构的情况下组装双极纺锤体和成膜体微管阵列。我们最近在拟南芥中的研究结果表明，AUGMIN亚基3（AUG 3），动物dim γ-微管蛋白3的同源物，在有丝分裂期间γ-微管蛋白依赖的MT成核和扩增中起着关键作用。在这里，我们报告分离的整个植物生长激素复合物，包含八个亚基。其中，AUG 1至AUG 6与动物对应物的序列相似性较低，但AUG 7和AUG 8仅与植物来源的蛋白质具有同源性。遗传分析表明，AUG 1、AUG 2、AUG 4和AUG 5基因是必需的，因为这些基因中的稳定突变只能传递给杂合植物。不育aug 7 -1纯合突变体，其中AUG 7的表达显着降低表现出多效性表型，严重阻碍营养和生殖生长。aug 7 -1突变导致有丝分裂纺锤体和成膜体中γ-微管蛋白的离域。因此，纺锤体被异常拉长，它们的极点无法收敛，因为MT被张开到离散的位置，从而呈现变形的阵列。此外，突变体成膜体通常具有边缘不均匀的无序MT束。我们的结论是MT阵列在植物有丝分裂过程中的组装取决于Augmin复合物，其中包括两个植物特异性亚基。
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 gamma-tubulin 3, plays a critical role in gamma-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 gamma-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.