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Previous studies of plant circadian clock evolution have often relied on clock models and genes defined in Arabidopsis. These studies identified homologues with seemingly conserved function, as well as frequent gene loss. In the present study, we aimed to identify candidate clock genes in the liverwort Marchantia polymorpha using a more unbiased approach. To identify genes with circadian rhythm we sequenced the transcriptomes of gemmalings in a time series in constant light conditions. Subsequently, we performed functional studies using loss-of-function mutants and gene expression reporters. Among the genes displaying circadian rhythm, a homologue to the transcriptional co-repressor Arabidopsis DE-ETIOLATED1 showed high amplitude and morning phase. Because AtDET1 is arrhythmic and associated with the morning gene function of AtCCA1/LHY, that lack a homologue in liverworts, we functionally studied DET1 in M. polymorpha. We found that the circadian rhythm of MpDET1 expression is disrupted in loss-of-function mutants of core clock genes and putative evening-complex genes. MpDET1 knock-down in turn results in altered circadian rhythm of nyctinastic thallus movement and clock gene expression. We could not detect any effect of MpDET1 knock-down on circadian response to light, suggesting that MpDET1 has a yet unknown function in the M. polymorpha circadian clock.

Factors regulating dynamics of chromatin structure have direct impact on expression of genetic information. Cohesin is a multi-subunit protein complex crucial for pairing sister chromatids during cell division, DNA repair and regulation of gene transcription and silencing. In non-plant species cohesin is loaded on chromatin by the Scc2/Scc4 (NIBPL/MAU2) complex. Here we identify AtSCC4, the Arabidopsis homolog of Scc4, and show that it forms a functional complex with AtSCC2, the homolog of Scc2. We demonstrate that AtSCC2 and AtSCC4 act in the same pathway and that both proteins are indispensable for cell fate determination during early stages of embryo development. Mutant embryos lacking either of these proteins develop only up to the globular stage, and show suspensor over-proliferation phenotype preceded by ectopic auxin maxima distribution. We further establish a new assay to reveal the AtSCC4-dependent dynamics of cohesin loading on chromatin in vivo. Our findings define Scc2/Scc4 complex as an evolutionary conserved machinery controlling cohesin loading and chromatin structure maintenance and provide new insight into plant-specific role of this complex in controlling cell fate during embryogenesis.

Factors regulating dynamics of chromatin structure have direct impact on expression of genetic information. Cohesin is a multi-subunit protein complex that is crucial for pairing sister chromatids during cell division, DNA repair and regulation of gene transcription and silencing. In non-plant species, cohesin is loaded on chromatin by the Scc2-Scc4 complex (also known as the NIBPL-MAU2 complex). Here, we identify the

The caspase‐related protease separase (EXTRA SPINDLE POLES, ESP) plays a major role in chromatid disjunction and cell expansion in Arabidopsis thaliana. Whether the expansion phenotypes are linked to defects in cell division in Arabidopsis ESP mutants remains elusive. Here we present the identification, cloning and characterization of the gymnosperm Norway spruce (Picea abies, Pa) ESP. We used the P. abies somatic embryo system and a combination of reverse genetics and microscopy to explore the roles of Pa ESP during embryogenesis. Pa ESP was expressed in the proliferating embryonal mass, while it was absent in the suspensor cells. Pa ESP associated with kinetochore microtubules in metaphase and then with anaphase spindle midzone. During cytokinesis, it localized on the phragmoplast microtubules and on the cell plate. Pa ESP deficiency perturbed anisotropic expansion and reduced mitotic divisions in cotyledonary embryos. Furthermore, whilst Pa ESP can rescue the chromatid nondisjunction phenotype of Arabidopsis ESP mutants, it cannot rescue anisotropic cell expansion. Our data demonstrate that the roles of ESP in daughter chromatid separation and cell expansion are conserved between gymnosperms and angiosperms. However, the mechanisms of ESP‐mediated regulation of cell expansion seem to be lineage‐specific., This work was supported by grants from the VR Swedish Research Council (to P.N.M. and P.V.B.), Pehrssons Fund (to P.V.B.), the Swedish Foundation for Strategic Research (to P.V.B.), the Olle Engkvist Foundation (to P.V.B.), the Knut and Alice Wallenberg Foundation (to P.V.B.), the August T. Larsson Foundation (to A.P.S. and P.V.B.), Hatch Grant WNP00826 (to A.P.S.), and a Spanish Ministry of Science and Innovation grant (AGL2010‐15684 to M.F.S). V.S‐V. was recipient of a FPI fellowship from the Spanish Ministry of Science and Innovation (BES‐2008‐003592).

Factors regulating dynamics of chromatin structure have direct impact on expression of genetic information. Cohesin is a multi-subunit protein complex crucial for pairing sister chromatids during cell division, DNA repair and regulation of gene transcription and silencing. In non-plant species cohesin is loaded on chromatin by the Scc2/Scc4 (NIBPL/MAU2) complex. Here we identify AtSCC4, the Arabidopsis homolog of Scc4, and show that it forms a functional complex with AtSCC2, the homolog of Scc2. We demonstrate that AtSCC2 and AtSCC4 act in the same pathway and that both proteins are indispensable for cell fate determination during early stages of embryo development. Mutant embryos lacking either of these proteins develop only up to the globular stage, and show suspensor over-proliferation phenotype preceded by ectopic auxin maxima distribution. We further establish a new assay to reveal the AtSCC4-dependent dynamics of cohesin loading on chromatin in vivo . Our findings define Scc2/Scc4 complex as an evolutionary conserved machinery controlling cohesin loading and chromatin structure maintenance and provide new insight into plant-specific role of this complex in controlling cell fate during embryogenesis.