AtNUF2 modulates spindle microtubule organization and chromosome segregation during mitosis.

The NDC80 complex is a conserved eukaryotic complex composed of four subunits (NUF2, SPC25, NDC80, and SPC24). In yeast and animal cells, the complex is located at the outer layer of the kinetochores, connecting the inner layer of the kinetochores and spindle microtubules (MTs) during cell division. In higher plants, the relationship of the complex with the MTs is still unclear. In this study, we characterized the biological function of a subunit of the Arabidopsis NDC80 complex, AtNUF2. It was found that AtNUF2 was widely expressed in various organs, especially in different stages of embryonic development. It was verified that AtNUF2 was localized on MTs with α-Tubulin during the mitotic cell cycle by immunohistochemical assay. Mutation of AtNUF2 led to severe mitotic defects, not only in embryo and endosperm, but also in seedlings, resulting in seed abortion and stagnanting seedling growth. Furthermore, the biological function of AtNUF2 was studied using the partial complement seedlings of the nuf2-3/-DD45;ABI3pro::AtNUF2 (nuf2-3/-DA ). The chromosome bridge and lagging chromatids, along with aberration of spindle MTs, occurred in the root apical meristem cells of nuf2-3/-DA , resulting in the stop of the root growth. Meanwhile, the direct binding of AtNUF2 and AtSPC25 with MTs was determined by a MT co-sedimentation assay in vitro. This study revealed the function and mechanism of AtNUF2 mediating mitosis through modulating spindle microtubule organization and ensuring chromosome segregation during embryo, endosperm, and root development in Arabidopsis, which laid the foundation for subsequent research of NDC80 complex.