PLK-1 tethered on BUB-1 directs CDC-20 kinetochore recruitment to ensure timelyembryonic mitoses

During mitosis chromosomes assemble kinetochores in order to dynamically couple with spindle microtubules (Cheeseman, 2014; Musacchio & Desai, 2017). Kinetochores also function as signaling hubs directing mitotic progression by recruiting and controlling the fate of the Anaphase Promoting Complex/Cyclosome (APC/C) activator CDC-20 (Lara-Gonzalez et al., 2017; Lara-Gonzalez, Pines, et al., 2021; Musacchio, 2015). Kinetochores either incorporate CDC-20 into checkpoint complexes that inhibit the APC/C or dephosphorylate CDC-20, which allows it to interact with and activate the APC/C (Kim et al., 2017; Lara-Gonzalez et al., 2017). The importance of these two CDC-20 fates likely depends on biological context. In somatic cells the major mechanism controlling mitotic progression is the spindle checkpoint. By contrast, progression through mitosis during the cell cycles of early embryos is largely checkpoint-independent (Clute & Masui, 1995; Duro & Nilsson, 2021; Gerhart et al., 1984; Zhang et al., 2015). Here, by manipulating CDC-20 phosphorylation status, we show that CDC-20 phosphoregulation controls mitotic duration in the C. elegans embryo and defines a checkpoint-independent temporal mitotic optimum for robust embryogenesis. Flux of CDC-20 through kinetochores for local dephosphorylation requires an ABBA motif on BUB-1 that directly interfaces with the structured WD40 domain of CDC-20 (Di Fiore et al., 2015; Diaz-Martinez et al., 2015; He et al., 2013; Kim et al., 2017). We show that a conserved "STP" motif in BUB-1 that docks the mitotic kinase PLK-1 (Qi et al., 2006) is also necessary to recruit CDC-20 to kinetochores and for timely mitotic progression. The kinase activity of PLK-1 is required for CDC-20 to localize to kinetochores and targets a site within the CDC-20-binding ABBA motif of BUB-1; phosphorylation of this site promotes BUB-1-CDC-20 interaction and mitotic progression. Thus, the BUB-1-bound pool of PLK-1 ensures timely mitosis during embryonic cell cycles by promoting CDC-20 recruitment to the vicinity of kinetochore-localized phosphatase activity.