Overexpression of a truncated CTF7 construct leads to pleiotropic defects in reproduction and vegetative growth in Arabidopsis

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 kinetochore, connecting the inner layer of the kinetochore and spindle microtubules (MTs) during cell division. In higher plants, the relationship of the NDC80 complex with MTs is still unclear. In this study, we characterized the biological function of AtNUF2, a subunit of the Arabidopsis NDC80 complex. We found that AtNUF2 is widely expressed in various organs, especially in different stages of embryonic development. It was verified that AtNUF2 co-localized with α-tubulin on MTs during mitosis by immunohistochemical assays. Mutation of AtNUF2 led to severe mitotic defects, not only in the embryo and endosperm, but also in seedlings, resulting in seed abortion and stagnating seedling growth. Furthermore, the biological function of AtNUF2 was studied using partially complemented nuf2-3/-^{DD45;ABI3pro::AtNUF2} (nuf2-3/-^DA ) seedlings. The chromosome bridge and lagging chromatids occurred in nuf2-3/-^DA root apical meristem cells, along with aberration of spindle MTs, resulting in blocked root growth. Meanwhile, the direct binding of AtNUF2 and AtSPC25 to MTs was determined by an MT co-sedimentation assay in vitro. This study revealed the function of AtNUF2 in mitosis and the underlying mechanisms, modulating spindle MT organization and ensuring chromosome segregation during embryo, endosperm, and root development, laying the foundation for subsequent research of the NDC80 complex.

In Favor of Establishment: Regulation of Chromatid Cohesion in Plants

In eukaryotic organisms, the correct regulation of sister chromatid cohesion, whereby sister chromatids are paired and held together, is essential for accurate segregation of the sister chromatids and homologous chromosomes into daughter cells during mitosis and meiosis, respectively. Sister chromatid cohesion requires a cohesin complex comprised of structural maintenance of chromosome adenosine triphosphatases and accessory proteins that regulate the association of the complex with chromosomes or that are involved in the establishment or release of cohesion. The cohesin complex also plays important roles in the repair of DNA double-strand breaks, regulation of gene expression and chromosome condensation. In this review, we summarize progress in understanding cohesion dynamics in plants, with the aim of uncovering differences at specific stages. We also highlight dissimilarities between plants and other eukaryotes with respect to the key players involved in the achievement of cohesion, pointing out areas that require further study.

The Opposing Actions of Arabidopsis CHROMOSOME TRANSMISSION FIDELITY7 and WINGS APART-LIKE1 and 2 Differ in Mitotic and Meiotic Cells

Sister chromatid cohesion, which is mediated by the cohesin complex, is essential for the proper segregation of chromosomes during mitosis and meiosis. Stable binding of cohesin with chromosomes is regulated in part by the opposing actions of CTF7 (CHROMOSOME TRANSMISSION FIDELITY7) and WAPL (WINGS APART-LIKE). In this study, we characterized the interaction between Arabidopsis thaliana CTF7 and WAPL by conducting a detailed analysis of wapl1-1 wapl2 ctf7 plants. ctf7 plants exhibit major defects in vegetative growth and development and are completely sterile. Inactivation of WAPL restores normal growth, mitosis, and some fertility to ctf7 plants. This shows that the CTF7/WAPL cohesin system is not essential for mitosis in vegetative cells and suggests that plants may contain a second mechanism to regulate mitotic cohesin. WAPL inactivation restores cohesin binding and suppresses ctf7-associated meiotic cohesion defects, demonstrating that WAPL and CTF7 function as antagonists to regulate meiotic sister chromatid cohesion. The ctf7 mutation only had a minor effect on wapl-associated defects in chromosome condensation and centromere association. These results demonstrate that WAPL has additional roles that are independent of its role in regulating chromatin-bound cohesin.