The cell cycle controls spindle architecture in Arabidopsis by activating the augmin pathway.

To ensure an even segregation of chromosomes during somatic cell division, eukaryotes rely on mitotic spindles. Here, we measured prime characteristics of the Arabidopsis mitotic spindle and built a three-dimensional dynamic model using Cytosim. We identified the cell-cycle regulator CYCLIN-DEPENDENT KINASE B1 (CDKB1) together with its cyclin partner CYCB3;1 as key regulators of spindle morphology in Arabidopsis. We found that the augmin component ENDOSPERM DEFECTIVE1 (EDE1) is a substrate of the CDKB1;1-CYCB3;1 complex. A non-phosphorylatable mutant rescue of ede1 resembled the spindle phenotypes of cycb3;1 and cdkb1 mutants and the protein associated less efficiently with spindle microtubules. Accordingly, reducing the level of augmin in simulations recapitulated the phenotypes observed in the mutants. Our findings emphasize the importance of cell-cycle-dependent phospho-control of the mitotic spindle in plant cells and support the validity of our model as a framework for the exploration of mechanisms controlling the organization of the eukaryotic spindle. [Display omitted] • Generation of a 3D simulation of the Arabidopsis spindle • B1-type CDKs together with a B3-type cyclin control spindle morphology via augmin • The requirement of augmin for spindle morphology is recapitulated by 3D simulations Romeiro Motta et al. show that spindle morphology is controlled by the phosphorylation of augmin performed by a cell-cycle regulator complex in Arabidopsis. By constructing a tridimensional simulation of the Arabidopsis mitotic spindle, combined with several experimental approaches, they show that changes in augmin activity largely impact spindle organization. [ABSTRACT FROM AUTHOR]