The Arabidopsis homolog of Scc4/MAU2 is essential for embryogenesis

Abstract

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 Arabidopsis homolog of Scc4, which we denote Arabidopsis thaliana (At)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 the suspensor overproliferation 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 the Scc2-Scc4 complex as an evolutionary conserved machinery controlling cohesin loading and chromatin structure maintenance, and provide new insight into the plant-specific role of this complex in controlling cell fate during embryogenesis.

Maize Dek15 Encodes the Cohesin-Loading Complex Subunit SCC4 and Is Essential for Chromosome Segregation and Kernel Development

“…In Arabidopsis (Arabidopsis thaliana), the scc4 mutation leads to endosperm defects and embryo lethality, similar to the effects of the scc2, smc1, and smc3 mutations (Liu Cm et al, 2002;Sebastian et al, 2009;Minina et al, 2017). SCC4 depletion leads to precocious sister chromatid separation (PSCS) during mitosis in yeast and animals (Ciosk et al, 2000;Seitan et al, 2006;Watrin et al, 2006); however, the function of SCC4 in plant cell mitosis remains unclear.…”

In Favor of Establishment: Regulation of Chromatid Cohesion in Plants

“…The predicted protein sequence of Arabidopsis SCC2 reveals a putative plant homeodomain (PHD) finger, a domain involved in chromatin organization and regulation of gene expression (Sebastian et al, 2009). Cytological analyses of T-DNA insertional lines Atscc2-2 , Atscc2-3 , Atscc4-1 and Atscc4-1 indicates that in these lines 25% of all embryos develop only up to the heart stage and show loss of bilateral symmetry, cell over-proliferation in the suspensor, and in the case of Atscc2-2 , over-proliferation of the endosperm (Minina et al, 2017). In Atscc4-1 and Atssc2-2 analysis of the distribution of the auxin-response reporter DR5rev::3xVENUS-N7 indicates that most of the reporter is confined to the basal cells of the suspensor, which is the opposite to the wild type, suggesting the existence of: (a) alterations in the embryogenic potential of the suspensor in the mutants, and (b) a role for both SCC4 and SCC2 in embryonic cell fate determination (Minina et al, 2017).…”

“…Cytological analyses of T-DNA insertional lines Atscc2-2 , Atscc2-3 , Atscc4-1 and Atscc4-1 indicates that in these lines 25% of all embryos develop only up to the heart stage and show loss of bilateral symmetry, cell over-proliferation in the suspensor, and in the case of Atscc2-2 , over-proliferation of the endosperm (Minina et al, 2017). In Atscc4-1 and Atssc2-2 analysis of the distribution of the auxin-response reporter DR5rev::3xVENUS-N7 indicates that most of the reporter is confined to the basal cells of the suspensor, which is the opposite to the wild type, suggesting the existence of: (a) alterations in the embryogenic potential of the suspensor in the mutants, and (b) a role for both SCC4 and SCC2 in embryonic cell fate determination (Minina et al, 2017). It was also found that SCC4 interacts stably with the N-terminus of SCC2 in planta and in baker’s yeast, but this interaction is not required for proper localization of SCC4 to the plant nucleus in Atscc2-2 (Minina et al, 2017).…”

“…In Atscc4-1 and Atssc2-2 analysis of the distribution of the auxin-response reporter DR5rev::3xVENUS-N7 indicates that most of the reporter is confined to the basal cells of the suspensor, which is the opposite to the wild type, suggesting the existence of: (a) alterations in the embryogenic potential of the suspensor in the mutants, and (b) a role for both SCC4 and SCC2 in embryonic cell fate determination (Minina et al, 2017). It was also found that SCC4 interacts stably with the N-terminus of SCC2 in planta and in baker’s yeast, but this interaction is not required for proper localization of SCC4 to the plant nucleus in Atscc2-2 (Minina et al, 2017). The authors interpreted both this finding and the colocalization of SCC4 with mitotic kleisin RAD21.3/SYN4 during interphase as an indication that Arabidopsis SCC4 may play a special role in the determination of sites for cohesin loading on chromatin (Minina et al, 2017).…”

“…It was also found that SCC4 interacts stably with the N-terminus of SCC2 in planta and in baker’s yeast, but this interaction is not required for proper localization of SCC4 to the plant nucleus in Atscc2-2 (Minina et al, 2017). The authors interpreted both this finding and the colocalization of SCC4 with mitotic kleisin RAD21.3/SYN4 during interphase as an indication that Arabidopsis SCC4 may play a special role in the determination of sites for cohesin loading on chromatin (Minina et al, 2017). Taken together all these results indicate that in Arabidopsis the SCC2 protein plays an important role during meiosis (Sebastian et al, 2009), while the SCC2/SCC4 complex regulates embryo and endosperm development with additional functions that are specific for each subunit (Minina et al, 2017).…”