Polo-like kinase 1 independently controls microtubule-nucleating capacity and size of the centrosome

Centrosomes are composed of a centriolar core surrounded by a pericentriolar material (PCM) matrix that docks microtubule-nucleating {gamma}-tubulin complexes. During mitotic entry, the PCM matrix increases in size and nucleating capacity in a process called centrosome maturation. Polo-like kinase 1 (PLK1) localizes to centrosomes and phosphorylates PCM matrix proteins to drive their self-assembly, which leads to PCM expansion; this expansion has been assumed to passively increase microtubule nucleation to support spindle assembly. Here, we show that PLK1 directly controls the generation of binding sites for {gamma}-tubulin complexes on the PCM matrix, independently of PCM expansion. Selective inhibition of PLK1-dependent {gamma}-tubulin docking leads to spindle defects and impaired chromosome segregation, without affecting PCM expansion, highlighting the importance of phospho-regulated centrosomal {gamma}-tubulin docking sites in spindle assembly. Inhibiting both {gamma}-tubulin docking and PCM expansion by mutating substrate target sites fully accounts for the actions of PLK-1 in transforming the centrosome during mitotic entry. Summary StatementPolo-like kinase 1-mediated physical expansion of centrosomes during mitotic entry is proposed to passively increase their microtubule nucleating capacity. Ohta et al. show instead that generation of microtubule-nucleating sites is directly controlled by Polo-like kinase 1, independently of centrosome size.