Organelles maintain spindle position in plant meiosis

Accurate positioning of spindles is a critical aspect of cell division as it ensures that each daughter cell contains a single nucleus. In many flowering plants, two meiotic chromosome separations occur without intervening cytokinesis, resulting in two spindles in one cell during the second division. Here we report a detailed examination of two mutants, jason (jas) and parallel spindle1 (ps1), in which disturbed spindle position during male meiosis II results in the incorporation of previously separated chromosome groups into a single cell. Our study reveals that an organelle band provides a physical barrier between the two spindles. The loss of a single protein, JAS, from this organelle band leads to its disruption and a random movement of the spindles. JAS is largely associated with vesicles in the organelle band, revealing a role for vesicles in plant meiosis and that cytoplasmic events maintain spindle position during the chromosome division. In many plants, male meiosis involves two rounds of chromosome separation without cell division, resulting in two spindles in a single cell. Here Brownfield et al. show that an organelle band acts as a physical barrier between the spindles to ensure accurate chromosome segregation.