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Temporal controlled degradation of key cell division proteins ensures a correct onset of the different cell cycle phases and exit from the cell division program. In light of the cell cycle, the Anaphase-Promoting Complex/Cyclosome (APC/C) is an important conserved multi-subunit ubiquitin ligase, marking targets for degradation by the 26S proteasome. However, whereas the APC/C has been studied extensively in yeast and mammals, only in the last decade has the plant APC/C started to unveil its secrets. Research results have shown the importance of the APC/C core complex and its activators during gametogenesis, growth, hormone signaling, symbiotic interactions, and endoreduplication onset. In addition, recently, the first plant APC/C inhibitors have been reported, allowing a fine-tuning of APC/C activity during the cell cycle. Together with the identification of the first APC/C targets, a picture emerges of APC/C activity being essential for many different developmental processes. [ABSTRACT FROM AUTHOR]

Summary: Background: At meiosis, two successive rounds of chromosome segregation lead to ploidy halving. This is achieved through a stepwise release of sister chromatid cohesion, along chromosome arms to allow homolog segregation at anaphase I and at centromeres to allow sister chromatid segregation at anaphase II. Cohesins, the protein complex that ensures cohesion, must then be protected at centromeres throughout meiosis, until the onset of anaphase II. Members of the Shugoshin protein family have been shown to protect centromeric cohesins at anaphase I, but much less is known about the protection of cohesion during interkinesis, the stage between meiosis I and meiosis II. Results: Here, we (1) show that both Arabidopsis SHUGOSHINs paralogs are required for complete protection of centromeric cohesins during meiosis I, without apparent somatic function, and (2) identified PATRONUS (PANS1), a novel protein required for protection of meiotic centromeric cohesion. Although AtSGO1 and AtSGO2 protect centromeric cohesion during anaphase I, PANS1 is required at a later stage, during interkinesis. Additionally, we identified PANS2, a paralog of PANS1, whose mutation is synthetically lethal with pans1 suggesting that PANS genes are also essential for mitosis. PANS1 interacts directly with the CDC27b and the CDC20.1 subunit of the Anaphase Promoting Complex (APC/C), in a manner suggesting that PANS1 could be both a regulator and a target of the APC/C. Conclusions: This study reveals that centromeric cohesion is actively protected at two successive stages of meiosis, by SHUGOSHINs at anaphase I and by PATRONUS at interkinesis. [Copyright &y& Elsevier]