Biology subjects

Cromer, L.

Publications and source records attributed to Cromer, L..

3 recordsLinked to original sources

bioRxiv2025

Monopolar orientation of kinetochores at meiosis is enforced by COHESINS and their regulators, CENP-C, and the deSUMOylase SPF2

The first division of meiosis is unique in its capacity to halve the ploidy of the future gametes. To this end, one key innovation compared to mitosis is the monopolar orientation of the pairs of sister kinetochores required for the proper separation of homologs at meiosis I. How monopolar orientation is imposed is unclear and seems to vary in eukaryotes. Here we performed a forward genetic screen in Arabidopsis thaliana, specifically designed to identify the molecular components imposing monopolar orientation, based on mutants ability to restore fertility in spo11 osd1 haploid plants. We show that monopolar orientation involves all four cohesin subunits (REC8, SCC3, SMC1, SMC3), the cohesion establishment factors CTF18 and DCC1, and the cohesin protectors SGO1/2 and PANS1, the inner kinetochore protein CENP-C, and the desumoylase SPF2. The mutants show bipolar orientation of achiasmatic chromosomes, but monopolar orientation is maintained in the presence of crossovers despite splitting of sister kinetochores at metaphase I and reduced levels of cohesin. Taken together, the findings demonstrate that cohesion establishment and protection, kinetochore function, and deSUMOylation, together with crossovers, enforce monopolar orientation in plants and support a cohesion-driven model of kinetochore orientation at meiosis I that is conserved across kingdoms.

cell biology↗

bioRxiv2023

Rapid meiotic prophase chromosome movements in Arabidopsis thaliana are linked to essential reorganization at the nuclear envelope

Meiotic rapid prophase chromosome movements (RPMs) require connections between the chromosomes and the cytoskeleton, involving SUN (Sad1/UNC-84)-domain-containing proteins at the inner nuclear envelope (NE). RPMs remain significantly understudied in plants, notably with respect to their importance in the regulation of meiosis. Here, we demonstrate that Arabidopsis thaliana meiotic centromeres undergo rapid (up to 500 nm/s) and uncoordinated movements during the zygotene and pachytene stages. RPMs are not affected by altered chromosome organization and recombination but are abolished in the double mutant sun1 sun2. We also document the changes in chromosome dynamics and nucleus organization during the transition from leptotene to zygotene, including telomere attachment to SUN-enriched NE domains, bouquet formation, and nucleolus displacement, all of which were defective in sun1 sun2. These results establish A. thaliana as a new model species for studying the functional implications of meiotic RPMs and demonstrate the mechanistic conservation of telomere-led RPMs in plants.

genetics↗

bioRxiv2019

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

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 homologues 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.

cell biology↗