PDF(Pubmed)
Abstract：
The spindle assembly checkpoint (SAC) ensures faithful chromosome segregation during cell division by monitoring kinetochore-microtubule attachment. Plants produce both sequence-conserved and diverged SAC components, and it has been largely unknown how SAC activation leads to the assembly of these proteins at unattached kinetochores to prevent cells from entering anaphase. In Arabidopsis thaliana, the noncanonical BUB3.3 protein was detected at kinetochores throughout mitosis, unlike MAD1 and the plant-specific BUB1/MAD3 family protein BMF3 that associated with unattached chromosomes only. When BUB3.3 was lost by a genetic mutation, mitotic cells often entered anaphase with misaligned chromosomes and presented lagging chromosomes after they were challenged by low doses of the microtubule depolymerizing agent oryzalin, resulting in the formation of micronuclei. Surprisingly, BUB3.3 was not required for the kinetochore localization of other SAC proteins or vice versa. Instead, BUB3.3 specifically bound to BMF3 through two internal repeat motifs that were not required for BMF3 kinetochore localization. This interaction enabled BMF3 to recruit CDC20, a downstream SAC target, to unattached kinetochores. Taken together, our findings demonstrate that plant SAC utilizes unconventional protein interactions for arresting mitosis, with BUB3.3 directing BMF3\'s role in CDC20 recruitment, rather than the recruitment of BUB1/MAD3 proteins observed in fungi and animals. This distinct mechanism highlights how plants adapted divergent versions of conserved cell cycle machinery to achieve specialized SAC control.
摘要：
纺锤体组装检查点（SAC）通过监测动粒-微管附着来确保细胞分裂过程中忠实的染色体分离。植物产生序列保守和发散的SAC成分，SAC激活如何导致这些蛋白质在未连接的动体上组装以防止细胞进入后期，这在很大程度上是未知的。在拟南芥中，在整个有丝分裂过程中，在动子上检测到非经典BUB3.3蛋白，与仅与未连接染色体相关的MAD1和植物特异性BUB1/MAD3家族蛋白BMF3不同。当BUB3.3因基因突变而丢失时，有丝分裂细胞经常进入后期，染色体错位，并在被低剂量的微管解聚剂oryzalin攻击后呈现滞后的染色体，导致微核的形成。令人惊讶的是,其他SAC蛋白的动粒定位不需要BUB3.3，反之亦然。相反，BUB3.3通过两个内部重复基序与BMF3特异性结合，这两个内部重复基序不是BMF3动子定位所必需的。这种相互作用使BMF3能够招募CDC20，一个下游的SAC目标，独立的动臂。一起来看,我们的发现表明，植物SAC利用非常规的蛋白质相互作用来阻止有丝分裂，随着BUB3.3指导BMF3在CDC20招募中的角色，而不是在真菌和动物中观察到的BUB1/MAD3蛋白的募集。这种独特的机制突出了植物如何适应保守细胞周期机制的不同版本以实现专门的SAC控制。
