An Arabidopsis Kinesin-14D Motor Is Associated with Midzone Microtubules for Spindle Morphogenesis

The acentrosomal spindle apparatus has kinetochore fibers organized and converged towards opposite poles, however mechanisms underlying the organization of these microtubule fibers into an orchestrated bipolar array are largely unknown. Kinesin-14D is one of the four classes of Kinesin-14 motors that are conserved from green algae to flowering plants. In Arabidopsisthaliana, three Kinesin-14D members displayed cell cycle-dependent distinct localization patterns on mitotic spindles microtubules. Notably, Kinesin-14D1 was enriched on the midzone microtubules of prophase and mitotic spindles and later persisted in the spindle and phragmoplast midzones. The kinesin-14d1 mutant had kinetochore fibers disengaged from each other during mitosis and exhibited hypersensitivity to the microtubule-depolymerizing herbicide oryzalin. Oryzalin-treated kinesin-14d1 mutant cells had discrete kinetochore fibers attached to chromosomes that failed to be aligned at the metaphase plate. Kinesin-14D1 localization and function are dependent on its motor activity and the novel malectin-like domain, by acting on selective microtubules in the midzone of prophase and metaphase spindles. Our findings revealed a novel Kinesin-14D1-dependent mechanism that regulates the organization of kinetochore fibers in acentrosomal spindles.