The γ-tubulin complex protein GCP6 is crucial for spindle morphogenesis but not essential for microtubule reorganization in Arabidopsis
The γ-tubulin complex protein GCP6 is crucial for spindle morphogenesis but not essential for microtubule reorganization in Arabidopsis
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DOI：
10.1073/pnas.1912240116
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发表时间：
2019-12
期刊：
影响因子：
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通讯作者：
Huiying Miao;Rongfang Guo;Junlin Chen;Qiao-mei Wang;Y. Lee;Bo Liu
中科院分区：
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作者：
Huiying Miao;Rongfang Guo;Junlin Chen;Qiao-mei Wang;Y. Lee;Bo Liu
意义γ-微管蛋白对于真核细胞产生新的微管是必不可少的，这些微管组装成像有丝分裂纺锤体一样的阵列，其功能依赖于与之形成复合体的蛋白质。在缺乏中心体的细胞中，新微管的产生依赖于γ-微管蛋白环复合体(γTURC)的形成。我们的实验揭示了在缺乏中心体的植物的有丝分裂细胞分裂过程中，微管的产生依赖于γ微管蛋白，但不依赖于γ微管。我们的结论是，γTurC在纺锤体极点组织中起着关键作用，但植物细胞在没有它的情况下仍然完成了细胞分裂。因此，在植物细胞中的这项工作在总体上促进了我们对无着丝体微管组织的了解。γ-微管蛋白通常与5个相关的γ-微管蛋白复合体蛋白(GCP2~GCP6)形成环状复合体，该γ-微管蛋白环复合体(γTURC)作为动植物微管(MT)成核的模板。虽然在大多数真核生物中，γTURC参与MT成核，但在真菌中，仅有γ-微管蛋白小复合体(γTUSC)与γ-微管蛋白+GCP2和GCP3组装在一起时，此类事件就会强烈地发生。为了探索γTURC是否是植物中唯一具有功能的γ-微管蛋白复合体，我们构建了2个GCP6基因突变体，编码拟南芥中γTURC的最大亚基。两个突变体都表现出相似的矮化营养生长和育性降低的表型。GCP6突变体组装了γTUSC，而野生型细胞则让GCP6与其他GCP结合产生γTURC。虽然γ-微管蛋白在纺锤体微管上的定位明显减弱，但仍可检测到该蛋白的存在。Gcp6细胞形成的纺锤体缺乏MT会聚和可辨认的极点，但它们成功地应对了MT解体的挑战，并能够完成有丝分裂和胞质分裂。我们的结果表明，γTURC不是γ-微管蛋白复合体在植物细胞中用于MT成核的唯一功能形式，并且γ微管蛋白依赖而不是γTURC非依赖的机制满足了MT成核的基本需要。此外，我们还发现γ的TURC功能对于纺锤形MT阵列的组装比对成膜体的组装更为关键。因此，我们的发现为无着丝体MT的成核和组织提供了洞察力。
Significance γ-Tubulin is essential for eukaryotic cells to produce new microtubules that are assembled into arrays like mitotic spindles, and its function depends on proteins that form complexes with it. In centrosome-lacking cells, the generation of new microtubules is dependent on formation of the γ-tubulin ring complex (γTuRC). Our experiments reveal γ-tubulin–dependent but γTuRC-independent phenomena of microtubule generation during mitotic cell division in the plants that lack the centrosome. We conclude that the γTuRC plays a critical role in spindle pole organization, but that plant cells still complete cell division in its absence. Therefore, this work in plant cells advances our knowledge of acentrosomal microtubule organization in general. γ-Tubulin typically forms a ring-shaped complex with 5 related γ-tubulin complex proteins (GCP2 to GCP6), and this γ-tubulin ring complex (γTuRC) serves as a template for microtubule (MT) nucleation in plants and animals. While the γTuRC takes part in MT nucleation in most eukaryotes, in fungi such events take place robustly with just the γ-tubulin small complex (γTuSC) assembled by γ-tubulin plus GCP2 and GCP3. To explore whether the γTuRC is the sole functional γ-tubulin complex in plants, we generated 2 mutants of the GCP6 gene encoding the largest subunit of the γTuRC in Arabidopsis thaliana. Both mutants showed similar phenotypes of dwarfed vegetative growth and reduced fertility. The gcp6 mutant assembled the γTuSC, while the wild-type cells had GCP6 join other GCPs to produce the γTuRC. Although the gcp6 cells had greatly diminished γ-tubulin localization on spindle MTs, the protein was still detected there. The gcp6 cells formed spindles that lacked MT convergence and discernable poles; however, they managed to cope with the challenge of MT disorganization and were able to complete mitosis and cytokinesis. Our results reveal that the γTuRC is not the only functional form of the γ-tubulin complex for MT nucleation in plant cells, and that γ-tubulin-dependent, but γTuRC-independent, mechanisms meet the basal need of MT nucleation. Moreover, we show that the γTuRC function is more critical for the assembly of spindle MT array than for the phragmoplast. Thus, our findings provide insight into acentrosomal MT nucleation and organization.