Faithful genome partition during cell division relies on proper congression of chromosomes to the spindle equator before sister chromatid segregation. Here we uncover a kinesin-7 motor, kinetochore-associated kinesin 1 (KAK1), that is required for mitotic chromosome congression in Arabidopsis. KAK1 associates dynamically with kinetochores throughout mitosis. Loss of KAK1 results in severe defects in chromosome congression at metaphase, yet segregation errors at anaphase are rarely observed. KAK1 specifically interacts with the spindle assembly checkpoint protein BUB3.3 and both proteins show interdependent kinetochore localization. Chromosome misalignment in BUB3.3-depleted plants can be rescued by artificial tethering of KAK1 to kinetochores but not vice versa, demonstrating that KAK1 acts downstream of BUB3.3 to orchestrate microtubule-based chromosome transport at kinetochores. Moreover, we show that KAK1’s motor activity is essential for driving chromosome congression to the metaphase plate. Thus, our findings reveal that plants have repurposed BUB3.3 to interface with a specialized kinesin adapted to integrate proper chromosome congression and checkpoint control through a distinct kinetochore design.

细胞分裂过程中忠实的基因组分配依赖于在姐妹染色单体分离之前染色体正确地代表纺锤体赤道。在这里，我们发现了驱动蛋白 7 马达，着丝粒相关驱动蛋白 1 （KAK1），这是拟南芥有丝分裂染色体会议所必需的。KAK1 在整个有丝分裂过程中与着丝粒动态结合。KAK1 的缺失导致中期染色体会议的严重缺陷，但很少观察到后期的分离错误。KAK1 与纺锤体组装检查点蛋白 BUB3.3 特异性相互作用，两种蛋白都显示出相互依赖的着丝粒定位。BUB3.3 耗尽植物中的染色体错位可以通过 KAK1 与着丝粒的人工拴系来挽救，但反之则不然，这表明 KAK1 在 BUB3.3 的下游发挥作用，在着丝粒处协调基于微管的染色体运输。此外，我们表明 KAK1 的运动活动对于驱动染色体会议到中期板至关重要。因此，我们的研究结果表明，植物已经重新利用 BUB3.3 与一种特殊的驱动蛋白连接，这种驱动蛋白适应于通过独特的着丝粒设计整合适当的染色体会议和检查点控制。