A cytological and functional framework of the meiotic spindle assembly checkpoint in Arabidopsis thaliana

The spindle assembly checkpoint (SAC) is a surveillance mechanism active during metaphase to prevent aneuploidy. The SAC is especially important during meiosis to maintain genome stability over generations and sustain fertility. However, despite its crucial role for reproduction and breeding, little is known about the plant meiotic SAC. Here, we present a cytological and functional framework of the SAC in male meiocytes of Arabidopsis thaliana. Using live-cell imaging, we have dissected the temporal association of SAC components with the kinetochore and have identified the three conserved kinases BMF1, MPS1 and AURORA as crucial regulators of the loading of BMF3 to kinetochores. Functionally characterizing core SAC components, we found that BUB3.3 has a predominant and previously not recognized role in chromosome congression. We suggest that BUB3.3 is involved in efficient kinetochore-microtubule interactions. Furthermore, the meiotic SAC is only active for a limited time under severe microtubule destabilizing conditions leading to the hypothesis that the relaxed nature of the meiotic SAC is a gateway to polyploidization and hence might contribute to genome evolution in plants.