In Favor of Establishment: Regulation of Chromatid Cohesion in Plants

Abstract

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.

Keywords: CTF7; DNA repair; PDS5; WAPL; cell division; meiosis; recombination; transposons.

FIGURE 1

Putative model of a plant cohesin ring. The presumptive Arabidopsis SMC1/SMC3 cohesin complex may tether sister chromatids, and its activity may be regulated positively by CTF7 and negatively by WAPL. Other regulators are the kleisin SCC1, the subunit SCC3, cohesin regulator PDS5 and SCC2/SCC4.

FIGURE 2

Schematic representation of plant cohesin dynamics during mitosis and meiosis. Cohesin complexes contribute to meiotic chromosome dynamics, since they influence on pairing (alignment of homologous chromosomes), synaptonemal complex (SC) formation (intimate association of homologous chromosomes), and recombination (DNA exchanges, reciprocal or not, between homologous sequences). During prophase I, sister chromatid cohesion and reciprocal exchanges (crossovers, COs) maintain the homologous chromosomes connected as a bivalent after the SC is disassembled. Afterward, cohesion is removed in two steps: from chromosome arms during first meiotic division and from centromeres during second meiotic division (top). During mitosis, the complexes might be involved in replication and segregation of chromatids (bottom).