ZmMTOPVIB enables DNA double-strand break formation and bipolar spindle assembly during maize meiosis.

The meiotic TopoVI B subunit (MTopVIB) plays an essential role in DSB formation in mouse, Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa), and recent work reveals rice MTopVIB also plays an unexpected role in meiotic bipolar spindle assembly, highlighting multiple functions of MTopVIB during rice meiosis. In this work, we characterized the meiotic TopVIB in maize (Zea mays; ZmMTOPVIB). The ZmmtopVIB mutant plants exhibited normal vegetative growth but male and female sterility. Meiotic DSB formation was abolished in mutant meiocytes. Despite normal assembly of axial elements, mutants showed severely affected synapsis and disrupted homologous pairing. Importantly, we showed that bipolar spindle assembly was also affected in ZmmtopVIB, resulting in triad and polyad formation. Overall, our results demonstrate that ZmMTOPVIB plays critical roles in DSB formation and homologous recombination. In addition, our results suggest the function of MTOPVIB in bipolar spindle assembly is likely conserved across different monocots.