Patronus is the elusive plant securin, preventing chromosome separation by antagonizing separase

Abstract

Chromosome distribution at anaphase of mitosis and meiosis is triggered by separase, an evolutionarily conserved protease. Separase must be tightly regulated to prevent the untimely release of chromatid cohesion and disastrous chromosome distribution defects. Securin is the key inhibitor of separase in animals and fungi, but has not been identified in other eukaryotic lineages. Here, we identified PATRONUS1 and PATRONUS2 (PANS1 and PANS2) as the Arabidopsis homologs of securin. Disruption of PANS1 is known to lead to the premature separation of chromosomes at meiosis, and the simultaneous disruption of PANS1 and PANS2 is lethal. Here, we show that PANS1 targeting by the anaphase-promoting complex is required to trigger chromosome separation, mirroring the regulation of securin. We showed that PANS1 acts independently from Shugosins. In a genetic screen for pans1 suppressors, we identified SEPARASE mutants, showing that PANS1 and SEPARASE have antagonistic functions in vivo. Finally, we showed that the PANS1 and PANS2 proteins interact directly with SEPARASE. Altogether, our results show that PANS1 and PANS2 act as a plant securin. Remote sequence similarity was identified between the plant patronus family and animal securins, suggesting that they indeed derive from a common ancestor. Identification of patronus as the elusive plant securin illustrates the extreme sequence divergence of this central regulator of mitosis and meiosis.

The synaptonemal complex imposes crossover interference and heterochiasmy inArabidopsis

“…Chromosome spreads were performed as previously described ( 89 ). Immunolocalization was performed on cells with preserved three-dimensional structures as described in ref.…”

The Role of Anaphase-Promoting Complex/Cyclosome (APC/C) in Plant Reproduction

“…More recently, PANS1/CMR1 has been elegantly shown as the Arabidopsis homolog of Securin (Cromer et al, 2019). Securin is an APC/C substrate in animals and fungi, involved in the control of the metaphase to anaphase transition and anaphase onset by inactivating the cohesion-cleaving enzyme, Separase (Marangos and Carroll, 2008).…”

“…Separase must be tightly regulated to prevent the precocious release of chromatid cohesion and a catastrophic chromosome separation. At the onset of Anaphase, the APC/C triggers the degradation of PANS1, releasing SEPARASE activity and allowing chromosome segregation (Cromer et al, 2019).…”

“…Furthermore, during meiosis depletion of PANS1 leads to the premature release of cohesion (Cromer et al, 2013). Expression of an APC/C-insensitive PANS1 abolishes cohesion release and chromatid separation, mimicking the depletion of SEPARASE (Liu and Makaroff, 2006;Cromer et al, 2019). Disruption of PANS1 is known to lead to the premature separation of chromosomes in meiosis, and the simultaneous depletion of PANS1 and PANS2 is lethal, showing to be essential for sister chromatid separation during meiosis.…”

“…Disruption of PANS1 is known to lead to the premature separation of chromosomes in meiosis, and the simultaneous depletion of PANS1 and PANS2 is lethal, showing to be essential for sister chromatid separation during meiosis. It was observed that in pans1 mutant, sister chromatid cohesion is lost before metaphase II, causing defects in chromosome segregation at meiosis II (Figure 2) (Cromer et al, 2019).…”