OsREC8 Is Essential for Chromatid Cohesion and Metaphase I Monopolar Orientation in Rice Meiosis

Abstract

The successful transmission of chromosomes during mitosis and meiosis relies on the establishment and subsequent release of cohesion between replicated chromatids. Cohesion is mediated by a four-subunit structural maintenance of chromosome complex, called cohesins. REC8 is a key component of this meiotic cohesion complex in most model organisms studied to date. Here, we isolated and dissected the functions of OsREC8, a rice (Oryza sativa) REC8 homolog, using two null Osrec8 mutants. We showed that OsREC8 encodes a protein that localized to meiotic chromosomes from approximately meiotic interphase to metaphase I. Homologous pairing and telomere bouquet formation were abnormal in Osrec8 meiocytes. Furthermore, fluorescent in situ hybridization experiments on Osrec8 meiocytes demonstrated that the mutation eliminated meiotic centromeric cohesion completely during prophase I and also led to the bipolar orientation of the kinetochores during the first meiotic division and accordingly resulted in premature separation of sister chromatid during meiosis I. Immunolocalization analyses revealed that the loading of PAIR2, PAIR3, OsMER3, and ZEP1 all depended on OsREC8. By contrast, the presence of the OsREC8 signal in pair2, pair3, Osmer3, and zep1 mutants indicated that the loading of OsREC8 did not rely on these four proteins. These results suggest that OsREC8 has several essential roles in the meiotic processes.

MEIOTIC F-BOX Is Essential for Male Meiotic DNA Double-Strand Break Repair in Rice

“…To further explore the role of MOF during meiosis, we performed immunolocalization on several rice SC-related proteins, including PAIR2, PAIR3, ZEP1, and REC8 in wild-type and mof male meiocytes. Rice REC8 is a cohesin critical for sister-chromatid cohesion, axial element formation, and homologous pairing (Shao et al, 2011). In mof, REC8 localization to chromosomes was identical to the wild type ( Figure 4) and thus was used as a marker for further meiotic analysis.…”

Replication Protein A2c Coupled with Replication Protein A1c Regulates Crossover Formation during Meiosis in Rice

“…In Arabidopsis and maize (Zea mays), homologs of REC8 are required for homologous pairing and recombination, largely by influencing the chromatin structure (Bhatt et al, 1999;Cai et al, 2003;Chelysheva et al, 2005;Golubovskaya et al, 2006). Rice REC8 was recently identified, and its depletion resulted in a lack of homologous pairing and failure to load key rice meiotic proteins, including PAIR2, PAIR3, MER3, and ZEP1, onto the chromosomes (Wang et al, 2009Shao et al, 2011). Therefore, it is reasonable to consider that REC8 may provide a platform for premeiotic recombination apparatus assembly.…”

“…Given that REC8 and RPA2c colocalize at S/ G2 phase and that loss of REC8 prevents loading of several key factors including PAIR3 and ZEP1 in rice (Shao et al, 2011), we performed dual immunolocalization to test whether depletion of RPA2c influences the normal loading of PAIR3 and ZEP1. Localization of PAIR3 and ZEP1 in rpa2c was indistinguishable to that in the wild type (see Supplemental Figures 5A and 5B online).…”

“…Dual immunolocalization was performed using the RPA2c antibody in combination with the centromere-specific histone H3 variant (CenH3) (Shao et al, 2011) in PMCs from a loss-of-function REC8 T-DNA insertion line (see Supplemental Figures 4A to 4C online). RPA2c foci were almost absent on chromosomes from interphase to zygotene in rec8, while bright CenH3 signals were clearly observed ( Figures 6A to 6C), suggesting that localization of RPA2c depends on loading of REC8.…”

“…REC8 and HOP1 are conserved across diverse species, and their homologs (At-REC8/At-SYN1/At-DIF1 [three names for the same gene] and Os-REC8 for REC8; ASY1 and PAIR2 for HOP1) have also been identified in Arabidopsis and rice. Depletion of REC8 causes chromosome fragmentation and formation of univalents (Cai et al, 2003;Chelysheva et al, 2005;Shao et al, 2011), and mutation of ASY1 and PAIR2 also results in defects in synapsis and CO formation in Arabidopsis and rice, respectively (Caryl et al, 2000;Nonomura et al, 2006;SanchezMoran et al, 2007).…”